A flake to set up the tooling to work with Zephyr through west

This is based on:

• https://github.com/maxhbr/myconfig/tree/d0a49d7d7313cd2867a59b6fbff3d80dfed5cb78/modules/dev.embedded.zephyr
• https://www.reddit.com/r/NixOS/comments/144iw0x/need_help_getting_zephyr_rtos_native_posix_target/
• https://gist.github.com/ejohnso49/cfa7c000f9b93c55b71be9116162b2a3
• https://github.com/tangybbq/non-c-on-zephyr/blob/main/shell.nix
• https://github.com/tangybbq/non-c-on-zephyr/blob/main/shell.nix