STM32: Add a low_level::Timer::wait_for_update function to timers

[EliteTK]

This is a new take on #4630.

I noticed there is now a mode thing in embassy-stm32 itself. The way I use it here is not quite how it's used elsewhere. I was trying to avoid a disruptive change to the low level timer constructor and to avoid requiring every user of this to pass every relevant IRQ binding.

You call with_update_interrupt on a Timer and this gives you a new Timer with a slightly different time indicating that the binding was passed. This unlocks wait_for_update. The idea is that capture compare and all the other timer specific interrupts could be added this way in the future without disrupting each other.

I believe this would eventually make the low-level timer driver powerful enough to implement any of the high level drivers from normal code without necessarily needing direct support from embassy-stm32.

I think this does a good job of addressing some of the comments from the previous PR discussion while staying relatively small as a change.

But I understand that the with_update_interrupt approach is somewhat unusual here... Interested to hear opinions.

[xoviat]

I am not sure whether it's a good idea to add mode to the low-level timers. In fact the low-level timers should be type-erased, but that's a big refactor.