message: op-node: ChannelOut doc comments
diff: @@ -87,10 +87,15 @@ func makeUVarint(x uint64) []byte {
  return tmp[:n]
  }
  +// ReadyBytes returns the number of bytes that the channel out can immediately output into a frame.
  +// Use `Flush` or `Close` to move data from the compression buffer into the ready buffer if more bytes
  +// are needed. Add blocks may add to the ready buffer, but it is not guaranteed due to the compression stage.
  func (co *ChannelOut) ReadyBytes() int {
  return co.buf.Len()
  }
  +// Flush flushes the internal compression stage to the ready buffer. It enables pulling a larger & more
  +// complete frame. It reduces the compression efficiency.
  func (co *ChannelOut) Flush() error {
  return co.compress.Flush()
  }
  