Function from_queued 

pub(crate) async fn from_queued(
    queued: QueuedConn,
    negotiated: &HashSet<ProtocolID>,
    proto_ids: impl IntoIterator<Item = ProtocolID> + Clone,
    task_group: &TaskGroup,
    stop_chan: Sender<Result<()>>,
) -> Result<Arc<dyn PeerConnection>>

Build the right PeerConnection for the post-handshake QueuedConn. Picks MuxConnection when QUIC is in use, SingleConnection otherwise.