Sleep support for esp32c3

[jneem]

This implements basic support for esp32c3 sleep. Only timer and GPIO are supported for wakeup so far.

I wrote this mostly by comparing the esp32s3 sleep implementation with the IDF source. I was a little confused by the RTCPinWithResistor trait, because as far as I could tell IDF configures pullup and pulldown on all the wakeup pins...

I had one question, though (which is probably caused by me being an embedded noob): what do you do to observe printlns when sleeping? espflash seems to just disconnect on deep sleep, and on light sleep it keeps the connection but doesn't actually print anything. I'm testing it right now using blinking leds...

Must

• The code compiles without errors or warnings.
• All examples work.
• cargo fmt was run.
• Your changes were added to the CHANGELOG.md in the proper section.
• You updated existing examples or added examples (if applicable).
• Added examples are checked in CI

Nice to have

• You add a description of your work to this PR.
• You added proper docs for your newly added features and code.

[jessebraham]

Thanks for the PR. Could you please remove all of the #[rustfmt::skip] attributes? I don't want to get in the habit of doing this, it's really not necessary and adds a lot of noise to the code.

[jessebraham]

(Also sorry, I will review this soon!)

[bjoernQ]

LGTM - Thanks for your contribution

[jessebraham]

I have apprehensions about having completely different RTCPin traits for RISC-V and Xtensa, but I think for the time being this is okay and probably implies we need to rethink that trait. Once we add support for more devices the path forward may become more clear, so we'll just roll with this for now I suppose.

Thanks for your work on this, LGTM!