My system configuration via Nix flakes

Add script to ensure Rust nightly version stays in sync

This was caused by rust-overlay's selectLatestNightlyWith silently pinning on the last nightly that included an out-of-date component. This won't stop that from happening, but should catch it much sooner.

Created by  finchie  on February 26, 2025
FU7S4JHV267EBWLMNE3B7EESCDEDLFJ67UMK75C76CSDONRY3OSAC
Change contents