Use Waker::clone_from internally

[yoshuawuyts]

Now that rust-lang/rust#96979 has been merged, we should use Waker::clone_from in our set_waker functions to remove reduce unnecessary clones. If done right, then from now on we'll typically only clone-on-wake the first time our concurrency types are polled.

This should be relatively simple to implement, so anyone who wants to pick it up should feel free to. It would also be interesting to bench this on nightly, which should have these changes starting ~tomorrow.