feat: add Big5Encoder (Unicode→Big5), bump to 1.2.0 - Big5Encoder mirrors Big5Decoder via a lazy reverse lookup over the existing mapping table; encode() throws on unmapped chars, encodeLossy() skips them. - Round-trip + known-byte + ASCII tests.
feat: add Big5Encoder (Unicode→Big5), bump to 1.2.0 - Big5Encoder mirrors Big5Decoder via a lazy reverse lookup over the existing mapping table; encode() throws on unmapped chars, encodeLossy() skips them. - Round-trip + known-byte + ASCII tests.