Flake for build Pico HSM/OpenPGP/Fido firmware

https://github.com/polhenarejos/pico-openpgp
https://github.com/polhenarejos/pico-hsm
https://github.com/polhenarejos/pico-fido

Currently only pico rp2040/2350 is supported.

TODO:

1. make build env for esp32

thanks leo60228: https://github.com/leo60228/nix-rp2040