Extract ML-KEM SIMD code to C

[franziskuskiefer]

We have working C code that is generally fast enought. There will be more changes needed but we'll track that as part of the integration processes.

The C code lives in libcrux-ml-kem/c now instead of hacl-packages because it is self-contained.

Follow-ups

• [ ] Add extraction to CI
• [ ] Add C code to CI

Fixes #268

[franziskuskiefer]

closing in favour of #296 that has a couple more changes.