Signature APIs

[wysiwys]

• Implement key-centric and slice-based signature public APIs for libcrux-ml-dsa, libcrux-ed25519, and libcrux-ecdsa
• Include macros in libcrux-traits crate that reduce boilerplate in signature API implementations in crates
• Add libcrux-signature crate
• Implement internal sign_mut() in libcrux-ml-dsa (moved from the change in Signature traits #1080 )
• Update changelogs
• Additional documentation as needed

Resolves #1034

[keks]

I think this looks pretty good! I left some comments for feedback. I also noticed that there are a few public items (I think just modules?) that do not have a doc comment, I guess these are what you had in mind with the documentation todo in the PR?

[keks]

To me the error type looks good - what were you thinking of here? I suppose we could define the error somewhere else and reuse it across modules?