Complete ML-KEM NIST KAT Test Vectors

[kevinamccorvon]

We're using placeholder tests instead of real NIST test vectors for ML-KEM. Check hpcrypt-mlkem/tests/kat_tests.rs - there are 5 TODOs where we need actual FIPS 203 test data.

Steps:

• Grab the official NIST FIPS 203 test vectors (ML-KEM-512, ML-KEM-768, ML-KEM-1024)
• Swap out placeholder tests with real KAT vectors
• Cover all parameter sets
• Add docs linking to test vector source

This is mandatory for FIPS 203 compliance and any certification work. Without real test vectors, we can't claim compliance.