Function spawn_demux_reader 

fn spawn_demux_reader(
    task_group: &TaskGroup,
    reader: FramedReader<PeerNetMsgCodec>,
    recv_queues: HashMap<ProtocolID, Arc<AsyncQueue<ProtocolEvent>>>,
    stop_chan: Sender<Result<()>>,
)

Spawn the single-pipe reader task. Reads PeerNetMsgs, routes Protocol payloads into the matching recv queue, signals the peer via stop_chan on Shutdown / error.