Add ETM tasks and events for timers

[sisoteuz]

I'd be happy to contribute implementing ETM tasks and events for timers. I've got a personal project going on an esp32-c6 dev kit for which I'd like to experiment with timers ETM.

As far as my seach has gone, I couldn't find such implementation in the HAL yet.

[bjoernQ]

Such a contribution would be very welcome!

We currently have support for SYSTIMER events and GPIO tasks and events.

Looking into those implementations should give you hints on how to implement the tasks and events for the general-purpose timers

[sisoteuz]

I've got a first draft that compiles for esp32-c6. There are some rough edges that I would be happy to receive feedback about.

I went with adding a const parameter to TimerGroupInstance that identifies the timer group number. This is used in the TimerEtmTasks and TimerEtmEvents to reduce code duplication and derive the channel number based on the timer group number.

I'm not entirely happy with that as it arguably introduces some breaking changes in other parts of the codebase, so I'm open to any suggestions, as I couldn't see any other alternative with my knowledge of rust.

I also added the example etm_timer.rs to showcase how all of this works.