Implements ChaChaPolySigil that applies pre-obfuscation before sending
data to CPU encryption routines. This ensures raw plaintext is never
passed directly to encryption functions.
Key improvements:
- XORObfuscator and ShuffleMaskObfuscator for pre-encryption transforms
- Nonce is now properly embedded in ciphertext, not stored separately
in headers (production-ready, not demo-style)
- Trix crypto integration with EncryptPayload/DecryptPayload methods
- Comprehensive test coverage following Good/Bad/Ugly pattern
