[ML-KEM] Support PQCP APIs

[franziskuskiefer]

Implement common APIs with the other PQCP projects.

See pq-code-package/tsc#4 (comment)

[jschneider-bensch]

Preserve current APIs behind e.g. a c-api feature, for consumers of the C extraction.

[franziskuskiefer]

• feature gate for "c-api" + deprecation warning + add c-api to default features
• check consumer (e.g. Signal using incremental)

[jschneider-bensch]

Adding the new features ( c-apis for the old API and pqcp for the common PQCP API) unfortunately blows up our CI when it comes to cargo hack checking all combinations of features.

[franziskuskiefer]

unfortunately blows up our CI when it comes to cargo hack checking all combinations of features.

Let's define a set of features we actually care about and only run those. Or add a depth, or use --each-feature instead.

[franziskuskiefer]

• public key validation
• reduce jobs run on CI
• Add crypto_kem_sk_from_seed, crypto_kem_pk_from_sk