embassy-rp (rp2040): Rtc wait_for_alarm

[1-rafael-1]

This PR adds the ability to wait for an RTC alarm.

Reviewer note:

• !!!Breaking change!!! due to the fact that Rtc struct new() fn now expects Irqs
• Implementation of binding interupt and handling waker inspired from adc.rs, this is my first time doing this, so I hope I got it reasonably right.
• I feel like I cheated because I used a flag to mark that we had an interrupt occur - i found no good documentation ad no good place in the Rtc registers to read the same fact from there, and a bunch of tests with that got me nowhere. In case this was rather unenlightened... let me know please!
• AI was used for syntax help and to answer my 100 questions on what stuff like compiler_fence does and how interrupts, wakers, ... work. Or in other words: Newbie mistakes are not unlikely.

I tested on a Pico board with the provided new example, so this works:

• wait_for_alarm no matter if one is yet scheduled yet or not
• alarm_scheduled can determine if we have an alarm sceduled or not and if we have we get the DateTimeFilter out of it.