Imap IDLE polling approach

Hi,

this is more a question than an issue itself. The current IDLE implementation is designed in a way that the future resolves for anything that comes from the server. I am wondering then what would be best approach for long IDLE polling, where client listens continuously for any change from the server side. I was thinking of a loop:
```
loop {
let (idle_wait, _interrupt) = idle.wait();
let idle_result = idle_wait.await.unwrap();
match idle_result {
...
};
}
```

The above approach calls [#wait](https://github.com/async-email/async-imap/blob/master/src/extensions/idle.rs#L100) each time and apart from that, there's a tiny possibility to miss server message when the current future is resolved and the execution is in the `match` statement. What would be best approach to tackle that?

Start with src/extensions/idle.rs at the wait method linked in the issue, then trace how the returned futures resolve and how server messages are handled. The issue is currently a design question rather than a defined implementation task; done would require an agreed approach and a concrete scope for changing or documenting long IDLE polling.

Written by the indexing model from the issue text.