embassy-nrf: New Event/Task types

[fnafnio]

So I've just tried the new updates and found no way to link up timer compare events to PPI, as ppi::Event is not implemented for the timer events and Event::from_reg is private.
Will Event::from_reg eventually become public or be implemented for the rest of the peripherals?
For now I will just make from_reg public and use it like in BufferedUarte, but I might be missing something

[Dirbaio]

The inner pointer in Task and Event is public, so you can implement a from_reg equivalent in your crate.

pub struct Task(pub NonNull<()>);
pub struct Event(pub NonNull<()>);

This is intentional, because I want to remove all references to the PAC from the public API, so it can be bumped or replaced without breaking the public API.

I'm aware short-term it's less usable. This would also be improved by implementing a Timer HAL in embassy.

(tldr of the reasons for that: We may switch to something else due to a few problems with the PAC design: slow compile, can only link one major version in the binary, almost all PAC changes are breaking so require a major version, the owned singletons can't be semver-tricked due to Deref impl, rust-embedded/wg#387, and for stm32 stm32-rs/meta#4)