refactor esp-wifi to ease using external task scheduler

[kaspar030]

Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
• My changes were added to the CHANGELOG.md in the proper section.
• I have added necessary changes to user code to the Migration Guide.
• My changes are in accordance to the esp-rs API guidelines

Extra:

• I have read the CONTRIBUTING.md guide and followed its instructions.

Pull Request Details 📖

Description

This is my attempt at using Ariel OS threads instead of the slim scheduler that ships with esp-wifi.

Mostly, this refactors the preempt & timer modules:

• the timer module is split into

  • time, providing the generic time functions)
  • radio, this has the previous radio isr setup stuff
  • preempt::timer, containing the task switching related timer setup

• all scheduler setup / teardown is now handled in preempt::setup() and preempt::disable().

• the radio ISRs are configured independently from that (the radio module now exposes the setup_radio_isr()/disable_radio_isr()

Basically, all task switching / scheduling code is split into preempt.
With that in place, replacing those guts with e.g., the Ariel scheduler is actually quite simple, by just disabling the preempt module and providing the functions elsewhere.

This is WIP, please ignore the OptionalPeripherals commit, and Im just importing the ariel code into preempt_custom.rs for local testing. I expect that integration to change. I've tested this with the old scheduler from esp-hal, and the hacked-in Ariel preempt_custom.rs`, on an s3 devkit.

I hope the refactoring and moving code is not too intimidating.
I was struggling a bit before the refactor. E.g., setup_timer_isr() was a bit overloaded, and it took a while to see what's used by the scheduler and whats needed elsewhere.
IIUC, at least this is not user-facing.

Let me know what you think, if this direction might be doable!

update I've rebased this on current main, and dropped the ariel support for now.

Testing

Describe how you tested your changes.

[kaspar030]

this function was identical for riscv and xtensa. the comments are a mix. I don't know which statements are true for either architecture.

[bugadani]

Nice, this change will probably make it simpler to just throw all this out in favour of esp_hal::time::* :)

[bjoernQ]

Very nice! Lots of things I wanted to do for quite some time - from my side this looks already mergeable

[bugadani]

Thanks!

[kaspar030]

Should I rebase this to main?

[bugadani]

No need, it will merge cleanly, just needs a +1 from someone else, ideally @bjoernQ :)

[jessebraham]

Changes LGTM, but will let Bjoern have the final say before merging. Thanks!

[bjoernQ]

Thanks!

[kaspar030]

Thanks for the quick review!