- Replace separate encrypt/decrypt with shared caesar() function
- Add direction constants (DIRECTION_ENCODE, DIRECTION_DECODE) and
prompts
- Update main.py to support interactive encode/decode loop
- Keep encrypt/decrypt as wrappers for backward compatibility
- Add tests for caesar() with both directions and error handling
- Update tests for main.py with interactive scenario tests
- Implement decrypt function that reverses encryption with negative
shift
- Export decrypt in package's public API
- Update tests with basic roundtrip and edge case tests
- Update documentation to reflect encryption/decryption support