Reduce size of Buffer polyfills

[pi0]

The Buffer polyfill we provided, is a much more compacted version of browserify Buffer that is used in most of the other implementations.

Although I have previously spend some time to optimize it, I belive it can be furhor more optimized in terms of both size and performance by migrating to more modern native APIs.

Steps:

• Add test suite for Buffer
• Enable typecheck on all buffer related files
• Get rid of old browser/js compact syntax and workarounds
• Investigate native integrations

(if you like to contribute, separate PR is welcome for each top-down ❤️ )