### Added
- Multi-Keyring implementation for composing multiple keyrings (#28)
- Support for generator keyring that generates plaintext data keys
- Support for child keyrings that wrap existing data keys
- wrap_key/2 function with generator + children chaining (fail-fast)
- unwrap_key/3 function with sequential keyring iteration (first-success)
- Comprehensive unit tests (31 tests) covering all edge cases
- Test vector validation for all 7 multi-RSA test vectors
- Nested multi-keyring support for complex key hierarchies
- Error collection when all keyrings fail during decryption
- Raw RSA keyring implementation with encrypt/decrypt support (#27)
- Support for all 5 padding schemes: PKCS1 v1.5, OAEP-SHA1/256/384/512
- PEM key loading for X.509 SubjectPublicKeyInfo and PKCS#8 PrivateKeyInfo
- wrap_key/2 function for encrypting data keys with RSA public keys
- unwrap_key/3 function for decrypting EDKs with RSA private keys
- Comprehensive unit tests (28 tests) and test vector validation (5 vectors)
- Edge case tests for unicode key names and empty encryption contexts
- MGF1 hash matching for OAEP padding per spec requirements
- :public_key application to extra_applications for OTP loading
### Changed
- Increased minimum code coverage requirement from 90% to 92%