[ML-KEM] Provide idiomatic Rust API & PQCP common API

[jschneider-bensch]

This PR attempts to provide an idiomatic Rust API for ML-KEM, as well as the PQCP common APIs.

• introduce default feature c-apis for old APIs
  • Add deprecation warning to old APIs
• Implement idiomatic Rust API for packed key generation, encapsulation, decapsulation. These will always perform key validation before encapsulation and decapsulation.
  • ML-KEM-512
  • ML-KEM 768
  • ML-KEM 1024
• Implement idiomatic Rust API for unpacked key generation, encapsulation, decapsulation. These will perform key validation once on deserialization and then perform encapsulation and decapsulation without further validation.
  • ML-KEM-512
  • ML-KEM 768
  • ML-KEM 1024
• Provide PQCP API on top of idiomatic API
  • ML-KEM-512 ??? I am not sure about crypto_kem_sk_from_seed and crypto_kem_pk_from_sk, specifically whether they should work for unpacked or packed keys.
  • ML-KEM 768
  • ML-KEM 1024
• Update all doc comments
• Update examples, benchmarks and tests to use new APIs

[dconnolly]

This is lovely to see 🎉