Add ML-KEM decapsulation validation test vectors

[sgmenda]

For aws/aws-lc#2891, I made some simple vectors to validate full decaps keys. I needed a new schema because the existing mlkem_test_schema.json only supports seed keys, and not full keys: https://github.com/C2SP/wycheproof/blob/main/schemas/mlkem_test_schema.json#L80-L84

[cpu]

Thanks! Would love to get another +1 review on this, but generally makes sense to me and doesn't seem like a good candidate for folding into existing test files/schemas.

[cpu]

Would love to get another +1 review on this

@sgmenda I chatted with Filippo about this OOB and he gave a verbal +1 to the PR but also suggested naming the test files to include "semi-expanded" (e.g. something like schemas/mlkem_semi_expanded_decaps_test_schema.json and testvectors_v1/mlkem_XXXX_semi_expanded_decaps_test.json). Are you open to that change? I think we can merge this afterwards.

[cpu]

Thanks!