Release HPKE draft support in v2.0.4

[mm9942]

Summary

• release crypt_guard, crypt_guard_proc, and crypt_guard_examples as v2.0.4
• preserve CGv2/HFv1 as explicit legacy compatibility framing rather than treating it as RFC 9180 HPKE
• add RFC 9180 Base-mode schedule/context coverage and pinned offline vectors
• add feature-gated, vector-verified experimental draft-ietf-hpke-pq-05 ML-KEM-768 and ML-KEM-1024 Base-mode profiles

Security and compatibility

The new public API is revision-named at crypt_guard::hpke_pq::draft_ietf_hpke_pq_05 and is available only with hpke-pq-draft-05. It keeps enc separate from ciphertexts, accepts direct AAD, owns nonce sequencing in non-cloneable contexts, and collapses altered enc, ciphertext, and AAD to authentication failure. The draft is explicitly documented as experimental and non-RFC-standardized.

Existing api::hpke::{seal, open} and crate-root hpke_seal / hpke_open remain CGv2/HFv1 compatibility APIs; no data is silently reinterpreted and there is no trial-decryption fallback.

Validation

• cargo fmt --check
• cargo clippy --lib -- -D warnings
• bash tests/vectors/verify_provenance.sh
• cargo test --test rfc9180_vectors
• cargo test --no-default-features --features hpke-pq-draft-05
• cargo test
• cargo test --workspace
• default and draft-feature doctests