docs: @Benchmark
    @BenchmarkMode(Mode.SampleTime)
    @OutputTimeUnit(TimeUnit.NANOSECONDS)
    public byte[][] marshalOld() {
      Metadata m = new Metadata();
      m.put(
          GrpcUtil.MESSAGE_ACCEPT_ENCODING_KEY,
          InternalDecompressorRegistry.getRawAdvertisedMessageEncodings(reg));
      return TransportFrameUtil.toHttp2Headers(m);
    }