Function send_after 

pub fn send_after<A, M, R>(
    actor_ref: &R,
    msg: M,
    delay: Duration,
) -> JoinHandle<()>
where
    A: Actor + Handler<M>,
    M: Message<Reply = ()>,
    R: ActorRef<A> + Clone + 'static,

Schedule a single message to be sent after delay.

Returns a JoinHandle that completes once the message has been sent (or the delay has elapsed and the actor is no longer reachable).