Function spawn_endpoint 

pub fn spawn_endpoint(
    protocol: Arc<AkkaProtocolTransport>,
    settings: RemoteSettings,
    remote: Address,
    remote_uid: u64,
    inbound_sink: UnboundedSender<InboundEnvelope>,
) -> EndpointHandle

Spawn an endpoint reader/writer pair. The returned handle is what RemoteActorRef::tell_serialized ultimately writes to.