Timeouts for blocking IO

[kevinmehall]

For Rust async, it's normal for futures not to have their own timeouts. To implement a timeout you race the future with a timeout future such that the main future will be cancelled if the timeout completes first. But this requires a reactor to provide timer functionality as a generic future, and I want to make nusb not require pulling in tokio or async-std for the common case where you don't actually need async in the rest of the app.

futures_lite::future::block_on is implemented on top of parking, which has an API with a timeout. So we could see if futures_lite would add a timeout (seems like many uses of blocking on async IO would want this?), find another implementation that has this to recommend, or copy that code here.

[XVilka]

It is definitely useful, given that libusb-rs provided this feature for transactions.