Fix PeripheralRef

[bugadani]

This PR applies the soundness fixes from embassy-hal-internal to our copy-pasted implementation, and modifies code where necessary to allow that change.

There are three noteworthy items:

• I've removed Peripheral: Sealed, as it is just in the way. Preventing the users from implementing the trait (e.g. like we do for Flex) doesn't give us much, I believe.
• I've removed a few InterruptConfigurable implementations from timers. I don't think we should implement that trait for peripheral singletons, we should keep it for peripheral drivers only.
• I've changed all methods on peripheral singletons to use &self. These are supposed to be singletons, and they shouldn't really have user-facing APIs anyway. &mut self wasn't really preventing anything anyway (e.g. we can race on GPIO configuration), but it was in the way of this PR.

Closes #2661 as we now have an identical implementation to embassy, except for a few custom additions where we abuse the pattern a bit.

[bjoernQ]

Thanks

[SergioGasquez]

LGTM! Thanks