docs: def _flush(self):
          """
          Flush the write buffers of the stream if applicable.
  
          In write mode, send the buffer content to the cloud object.
          """
          # Flush buffer to specified range
          buffer = self._get_buffer()
          start = self._buffer_size * (self._seek - 1)
          end = start + len(buffer)
  
          future = self._workers.submit(
              self._flush_range, buffer=buffer, start=start, end=end)
          self._write_futures.append(future)
          future.add_done_callback(partial(self._update_size, end))