add sleep to bun shell builtins

[dylan-conway]

What does this PR do?

fixes bun: command not found: sleep in ci

How did you verify your code works?

added tests

[robobun]

❌ @dylan-conway, your commit b7128ed has 12 failures in #3242:

test/js/bun/http/serve-body-leak.test.ts - 1 failing on 🪟 x64

test/integration/expo-app/expo.test.ts - 1 failing on 🪟 x64

test/integration/expo-app/expo.test.ts - 1 failing on 🪟 x64-baseline

test/cli/watch/watch.test.ts - timeout on 🪟 x64

test/cli/watch/watch.test.ts - timeout on 🪟 x64-baseline

test/regression/issue/07500/07500.test.ts - 1 failing on 🪟 x64-baseline

test/regression/issue/07500/07500.test.ts - 1 failing on 🪟 x64

test/cli/install/registry/bun-install-registry.test.ts - 1 failing on 🪟 x64

test/cli/install/registry/bun-install-registry.test.ts - 1 failing on 🪟 x64-baseline

test/js/web/streams/streams.test.js - 1 failing on 🍎 14 x64

test/js/bun/spawn/spawn.test.ts - timeout on 🪟 x64-baseline

test/cli/hot/watch.test.ts - 1 failing on 🪟 x64

test/cli/hot/watch.test.ts - 1 failing on 🪟 x64-baseline

test/cli/hot/hot.test.ts - 2 failing on 🪟 x64

test/cli/hot/hot.test.ts - 2 failing on 🪟 x64-baseline

test/js/bun/spawn/spawn-streaming-stdin.test.ts - 1 failing on 🪟 x64

test/js/bun/spawn/spawn-streaming-stdin.test.ts - 1 failing on 🪟 x64-baseline

test/js/bun/shell/shell-hang.test.ts - 1 failing on 🪟 x64-baseline

test/bundler/bun-build-api.test.ts - 1 failing on 🪟 x64

test/bundler/bun-build-api.test.ts - 1 failing on 🪟 x64-baseline

[dylan-conway]

need to change this to be non-blocking