Devtools: Reorganize submodules to be more ... modular

modules/programs/development-tools/rust.nix

@@ -6,7 +6,7 @@
     };
   };
 
-  flake.modules.nixos.development-tools = { pkgs, ... }: {
+  flake.modules.nixos.rust-dev = { pkgs, ... }: {
     nixpkgs.overlays = [
       inputs.rust-overlay.overlays.default
     ];