Function optionally_timeout 

fn optionally_timeout<'f, R, F>(
    runtime: &R,
    future: F,
    timeout: Option<Duration>,
) -> Pin<Box<dyn FusedFuture<Output = Result<F::Output, TimeoutError>> + Send + 'f>>
where
    R: Runtime,
    F: Future + Send + 'f,

Wrap a Future with an optional timeout.

If timeout is Some, returns a Timeout that resolves to the value of future if the future completes within timeout, or a TimeoutError if it does not. If timeout is None, returns a new future which maps the specified future’s output type to a Result::Ok.