Add 128-bit IV type using secret_block! macro with:
- Parsing from hex/binary/ASCII strings
- Conversions to/from Block128 for XOR operations
- Big-endian byte array conversions
Move duplicated macro definitions from aes and des crates into
cipher-core for shared use. Both macros now:
- Support u8 through u128 integer types
- Include Zeroize derive for secure memory handling
- Generate consistent formatting and conversion methods