Implement async Wait traits from embedded-hal-async

[dberlin]

This patch implements the embedded-hal-async Wait trait, which enables
waiting on an level/edge for pins in an async fashion.

It has been tested on multiple esp32s3 devices in production

[dberlin]

Not sure why cargo fmt errors out on the trailing whitespace in the allow, but i fixed it.

I also have a version of this that uses AtomicWaker instead of RefCell<Optional>, which is simpler, and doesn't require disabling interrupts to set the waker.
This is how basically all the other HAL's you will find do it - some form of atomic waker storage.

It is also Sync, and the current solution is only Send because of RefCell.

The downside is it requires the futures crate (or we have to copy the impl or find another).

I would guess as more and more async is implemented, the likelihood you need futures at some point anyway is high.
You can also feature disable basically all of it (we only need async-io feature).

But it's your show :)

Let me know if you want me to update this to the AtomicWaker version or not.

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[MabezDev]

Thanks for the PR! I have a few comments I think that should be addressed before we merge this :).

[dberlin]

I've updated to use notifications.

If you make one function in channel-bridge's Notification class public (poll_wait) we can reuse the crate.
It's actually the only one we need, so right now, i've copied your implementation and made that function accessible.

Let me know if you want me to make it not do anything until the first poll.

[MabezDev]

Thanks for this! Looks good to me :)

[ivmarkov]

@MabezDev This PR is very close to completion but still needs a few final small touches before merging. Given that the submitter might have moved after our strong disagreement what to do on pin drop I might be looking into it, but it will take some time. In any case, no rush - if you have time these days, you can of course also address my last set of comments.

[MabezDev]

I think I've addressed everything in the latest commit.

[ivmarkov]

Let's push it then?