message: Add nixpkgs-fmt to devShells
diff: let
  # Creates a development shell using a specific Rust toolchain
  createShell = { rust }: pkgs.mkShell {
  - packages = [ (rust.override { extensions = [ "rust-src" "rustfmt" ]; }) ];
  + packages = [
  + (rust.override { extensions = [ "rust-src" "rustfmt" ]; })
  + pkgs.nixpkgs-fmt
  + ];
  # Certain tools like `rust-analyzer` won't work without this
  RUST_SRC_PATH = "${rust}/lib/rustlib/src/rust/library";
  };
  