Explore fn_traits and tuple_trait to see if we can implement some cool

[Xuanwo]

fn_traits and tuple_trait can allow us to implement something like:

impl<B, T, E, Fut, FutureFn, Args> Retryable<B, T, E, Fut, FutureFn> for FutureFn
where
    B: BackoffBuilder,
    Fut: Future<Output = Result<T, E>>,
    FutureFn: FnMut(Args) -> Fut,
    Args: Tuple,
{
    fn retry(self, builder: &B) -> Retry<B::Backoff, T, E, Fut, FutureFn, Args> {
        Retry::new(self, builder.build())
    }
}

We can try to explore so that we can retry a function with args.