implement FusedStream for Receiver

[fogti]

as Receiver can detect if the channel is closed, it probably can implement FusedStream...
see also concurrent_queue::ConcurrentQueue::is_closed

[fogti]

impl<T> FusedStream for Receiver<T> {
    fn is_terminated(&self) {
        self.channel.queue.is_closed() && self.channel.queue.is_empty()
    }
}

[ghost]

I'm curious: in what cases is FusedStream useful or used in practice?

This sounds good - just a small correction: the Receiver is terminated when the queue is closed and is empty.

[fogti]

It is i.a. used for using the futures::select! macro without needing to .fuse() the Stream.

[fogti]

As FusedStream is defined in futures-core, this wouldn't even require another dependency. It would be a really small change which increases usability.