message: Add logging statements
diff: @@ -302,6 +302,7 @@ struct downstream_msg_visitor {
  template <class T>
  intrusive::task_result operator()(T& x) {
  + CAF_LOG_TRACE(CAF_ARG(x));
  auto& inptr = q_ref.policy().handler;
  if (inptr == nullptr)
  return intrusive::task_result::stop;
  @@ -320,6 +321,7 @@ struct downstream_msg_visitor {
  qs_ref.erase_later(dm.slots.receiver);
  selfptr->erase_stream_manager(dm.slots.receiver);
  if (mgr->done()) {
  + CAF_LOG_DEBUG("path is done receiving and closes its manager");
  selfptr->erase_stream_manager(mgr);
  mgr->stop();
  }
  