- EncryptionKey: remove Clone (move-only per spec), add custom redacting
Debug impl, make new() private (cfg(test)), add pub(crate) key_bytes()
accessor, make encrypt/decrypt pub(crate) module-internal helpers
- CachedKey: refactor to wrap DerivedKey (per service.md) with cached_at
and last_accessed fields; add key_type()/private_key()/public_key()
accessors
- Mnemonic: store validated Bip39Mnemonic to eliminate unwrap() in
to_seed(); enable bip39 zeroize feature so inner is zeroized on drop
- Fix clippy: remove unused import in drop_tracker tests, use struct
init syntax instead of field reassignment with Default
- Move low-level EncryptionKey round-trip/wrong-key tests from
integration tests to unit tests (encrypt/decrypt now pub(crate))