Store settings on module flash

[JohnAZoidberg]

Store settings in flash so they can persist module reset.

Resources:

• RP2040
  • https://github.com/jannic/rp2040-flash
  • https://www.makermatrix.com/blog/read-and-write-data-with-the-pi-pico-onboard-flash/
  • Best if we first try to make the firmware run from RAM: https://stackoverflow.com/questions/75314954/rpi-pico-write-to-flash-in-rust
  • https://kevinboone.me/picoflash.html?i=2
  • https://github.com/NegasonicX/Raspberry-PICO2040-Flash-Storage
• Generic
  • https://www.st.com/resource/en/application_note/an3969-eeprom-emulation-in-stm32f40xstm32f41x-microcontrollers-stmicroelectronics.pdf
  • https://github.com/qmk/qmk_firmware/blob/master/quantum/wear_leveling/wear_leveling.c