Phew.

This was mostly blocked by Micropython, but it has since then also
upgraded to IDF 5: https://github.com/micropython/micropython/commit/e4650125b88a35f074097f16d84a8f49bd22ac06

We take that change and selectively apply it where necessary. However,
it's not a 1:1 patch apply, as we already were on a somewhat forked
Micropython, and we also want to support IDF 5.1, not 5.0.

We also bump up the IDF distribution brought in by Nix, and fix some
warnings that have since turned into errors due to toolchain changes.

This is replaced by more mpy-centric code for user interaction plus
bl00mbox for the actual sound framework.

We already moved LEDs to their own task. Let's try doing that for
jacksense too. As long as we don't run out of RAM this should be better
than having larger tasks, as things won't block eachother that much..?

1. Add locking (st3m_audio_* functions are now thread/task-safe).
2. Remove some duplicate code around speaker/headphones output.
3. Simplify applying audio volume to codec ('apply' function).
4. Small style stuff (bool, etc).

This moves all I2C addresses and locking logic into the BSP.

Removes sdkconfig.p* files, use a single sdkconfig.defaults.

This is now 'overlaid' with flow3r-specific options by idf_ext.py.

This seem to break mpremote mount, and I'm not sure why we even want
them.