Expose vector retrieval by key in Swift & Objective-C libraries

[brittlewis12]

Thank you for the fantastic library, @ashvardanian! I'm using it quite happily for a couple different projects, and I'm excited for the opportunity to contribute back in a small way.

This PR adds two new features to the Swift & Obj-C libraries:

1. vector retrieval by key (get)
2. constructing indexes with multi-vector keys enabled

& add tests to exercise the new get interfaces & multi configuration on the swift side.

a couple notes:

• for the multi case:
  • the obj-c side doesn't do any work to break up the single large vector if a count greater than one is returned. this mirrors the cpp seam.
  • the swift seam returns a 2d array instead.
• there's a bit of duplication in the get implementations, both on the objective-c and on the swift side
• the swift 'sugar' interfaces are a bit less than ergonomic than they could be, requiring explicit typing on the expected return value at the callsite, since the parameters alone aren't enough to disambiguate. didn't think it was worth going further without feedback

---

tests are passing locally:

❯ swift build && swift test -v
Building for debugging...
[2/2] Emitting module USearch
Build complete! (0.87s)
Planning build
Building for debugging...
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -module-name USearch -incremental -emit-dependencies -emit-module -emit-module-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearch.swiftmodule -output-file-map /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearch.build/output-file-map.json -parse-as-library -c /Users/tito/code/usearch/swift/Index+Sugar.swift /Users/tito/code/usearch/swift/USearch.swift -I /Users/tito/code/usearch/.build/arm64-apple-macosx/debug -target arm64-apple-macosx10.13 -swift-version 5 -v -enable-batch-mode -index-store-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/index/store -Onone -enable-testing -g -j10 -DSWIFT_PACKAGE -DDEBUG -Xcc -fmodule-map-file=/Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchObjective.build/module.modulemap -Xcc -I -Xcc /Users/tito/code/usearch/objc/include -module-cache-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/ModuleCache -parseable-output -parse-as-library -emit-objc-header -emit-objc-header-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearch.build/USearch-Swift.h -color-diagnostics -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -F /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -I /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -L /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -Xcc -isysroot -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -Xcc -F -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -Xcc -fPIC
Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx10.13
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc -module-name USearchTests -incremental -emit-dependencies -emit-module -emit-module-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.swiftmodule -output-file-map /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.build/output-file-map.json -parse-as-library -c /Users/tito/code/usearch/swift/Test.swift -I /Users/tito/code/usearch/.build/arm64-apple-macosx/debug -target arm64-apple-macosx13.0 -swift-version 5 -v -enable-batch-mode -index-store-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/index/store -Onone -enable-testing -g -j10 -DSWIFT_PACKAGE -DDEBUG -Xcc -fmodule-map-file=/Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchObjective.build/module.modulemap -Xcc -I -Xcc /Users/tito/code/usearch/objc/include -module-cache-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/ModuleCache -parseable-output -parse-as-library -color-diagnostics -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -F /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -I /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -L /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -Xcc -isysroot -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -Xcc -F -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -Xcc -fPIC
Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx13.0
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file /Users/tito/code/usearch/swift/Test.swift -emit-dependencies-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.build/Test.d -emit-reference-dependencies-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.build/Test.swiftdeps -target arm64-apple-macosx13.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -stack-check -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -I /Users/tito/code/usearch/.build/arm64-apple-macosx/debug -I /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -F /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -color-diagnostics -enable-testing -g -module-cache-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/ModuleCache -swift-version 5 -Onone -D SWIFT_PACKAGE -D DEBUG -new-driver-path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-driver -empty-abi-descriptor -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -Xcc -fmodule-map-file=/Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchObjective.build/module.modulemap -Xcc -I -Xcc /Users/tito/code/usearch/objc/include -Xcc -isysroot -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -Xcc -F -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -Xcc -fPIC -module-name USearchTests -disable-clang-spi -target-sdk-version 14.2 -target-sdk-name macosx14.2 -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/local/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -parse-as-library -o /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.build/Test.swift.o -index-store-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/index/store -index-system-modules
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -emit-module -experimental-skip-non-inlinable-function-bodies-without-types /Users/tito/code/usearch/swift/Test.swift -target arm64-apple-macosx13.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -stack-check -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -I /Users/tito/code/usearch/.build/arm64-apple-macosx/debug -I /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib -F /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -color-diagnostics -enable-testing -g -module-cache-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/ModuleCache -swift-version 5 -Onone -D SWIFT_PACKAGE -D DEBUG -new-driver-path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-driver -empty-abi-descriptor -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -Xcc -fmodule-map-file=/Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchObjective.build/module.modulemap -Xcc -I -Xcc /Users/tito/code/usearch/objc/include -Xcc -isysroot -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -Xcc -F -Xcc /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks -Xcc -fPIC -module-name USearchTests -disable-clang-spi -target-sdk-version 14.2 -target-sdk-name macosx14.2 -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/local/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -emit-module-doc-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.swiftdoc -emit-module-source-info-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.swiftsourceinfo -emit-dependencies-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.build/USearchTests.emit-module.d -parse-as-library -o /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.swiftmodule -emit-abi-descriptor-path /Users/tito/code/usearch/.build/arm64-apple-macosx/debug/USearchTests.abi.json
Build complete! (0.56s)
Test Suite 'All tests' started at 2024-08-03 00:47:41.055.
Test Suite 'USearchPackageTests.xctest' started at 2024-08-03 00:47:41.057.
Test Suite 'Test' started at 2024-08-03 00:47:41.057.
Test Case '-[USearchTests.Test testUnit]' started.
Test Case '-[USearchTests.Test testUnit]' passed (0.001 seconds).
Test Case '-[USearchTests.Test testUnitMulti]' started.
Test Case '-[USearchTests.Test testUnitMulti]' passed (0.000 seconds).
Test Suite 'Test' passed at 2024-08-03 00:47:41.058.
	 Executed 2 tests, with 0 failures (0 unexpected) in 0.001 (0.001) seconds
Test Suite 'USearchPackageTests.xctest' passed at 2024-08-03 00:47:41.058.
	 Executed 2 tests, with 0 failures (0 unexpected) in 0.001 (0.001) seconds
Test Suite 'All tests' passed at 2024-08-03 00:47:41.058.
	 Executed 2 tests, with 0 failures (0 unexpected) in 0.001 (0.002) seconds

ran swift-format locally as well; more than happy to adjust anything as you see fit!

[ashvardanian]

Thanks for a great quality contribution @brittlewis12 🤗