#3 adds support for detecting disconnections through a custom Arc<AtomicBool>. This is not particularly efficient, but it works.

https://docs.rs/async-channel/1.1.1/async_channel/'s channels have a Sender that returns an error on disconnect; exactly as we would expect here. We should use this instead of our custom AtomicBool impl. async-std is expected to move over to this as well in the near future, but we shouldn't wait for that.

@jbr could you pick this up?