Unpacked API for ML-KEM

[karthikbhargavan]

This PR adds an unpacked API for the three variants of ML-KEM (512, 768, 1024) and for the three platforms we support (avx2, neon, portable). There is no generic multiplexing API for this, since the unpacked API exposes internal state which is different for the three platforms.

[franziskuskiefer]

Please add documentation to the public APIs. You can also add a warn(missing_docs) to the crate to show the places. We need that anyway.

[franziskuskiefer]

df8b66e is not the change that will make this work. The abstraction is required for the extraction, and exposing internal traits is generally a bad idea.
To make it work, you need to add the bounds to all types, as done 768. That way C extraction goes through, you can suppress the Rust warning until we have fixed the tools.

[karthikbhargavan]

Thanks, will aim to address all of these by the weekend.

[karthikbhargavan]

I think I fixed everything, but still need to merge the C code conflicts.

[karthikbhargavan]

Merged, resolved conflicts, regenerated C code.

[karthikbhargavan]

Please add documentation to the public APIs. You can also add a warn(missing_docs) to the crate to show the places. We need that anyway.

Done

Review re-requested

[franziskuskiefer]

Thanks! lgtm with a few final nits.

Looks like there are a mlkem768.cc~ files that shouldn't be there.

Review re-requested

[franziskuskiefer]