docs: def _packet_manager(self):
          """ Watch packet list for timeouts. """
          while True:
              if self._packets:
                  with self._packet_lock:
                      now = time.time()
  
                      self._packets[:] = \
                          [packet for packet in self._packets
                           if self._packet_timeout(packet, now)]
  
              # c.f. nyquist
              time.sleep(ACK_RESEND / 2)