startChunkedConversion method
Start a chunked conversion using the options given to the ZstdEncoder constructor.
While it accepts any Sink taking List's,
the optimal sink to be passed as sink is a ByteConversionSink.
Implementation
@override
ByteConversionSink startChunkedConversion(Sink<List<int>> sink) {
  final byteSink = asByteSink(sink);
  return _ZstdEncoderSink._(
      byteSink, level, inputBufferLength, outputBufferLength);
}