refactor: clean up scripts

Tidy up the script logic and deduplicate it a bit.

scripts/default.nix

@@ -37,12 +37,12 @@ let
 in
 {
   # Add scripts to overlay
-  flake.overlays.scripts = _final: prev: builtins.mapAttrs (callRustPackage prev) packages;
+  flake.overlays.scripts = _final: prev: builtins.mapAttrs (callRustPackage prev);
 
   # Add scripts to packages
   perSystem =
     { pkgs, ... }:
     {
-      packages = builtins.mapAttrs (callRustPackage pkgs) packages;
+      packages = builtins.mapAttrs (callRustPackage pkgs);
     };
 }