Add helper functions for multi-user toggle support

Introduced a new file `lib.nix` containing helper functions to streamline user package management and attributes for multi-user configurations. Updated various modules to utilize these functions, enhancing code maintainability and readability.

modules/apps/misc.nix

@@ -8,17 +8,15 @@
   options.my.apps.misc.enable = lib.mkEnableOption "miscellaneous desktop applications";
   config = lib.mkIf config.my.apps.misc.enable {
     users.users = let
-      users = if lib.isString config.my.toggleUsers.apps then [ config.my.toggleUsers.apps ] else config.my.toggleUsers.apps;
+      userLib = import ../lib.nix { inherit lib; };
       packages = builtins.attrValues {
-      inherit (pkgs)
-        blanket # background noise
-        metadata-cleaner # remove any metadata and geolocation from files
-        pika-backup # backups
-        gnome-obfuscate # censor private information
-        ;
+        inherit (pkgs)
+          blanket # background noise
+          metadata-cleaner # remove any metadata and geolocation from files
+          pika-backup # backups
+          gnome-obfuscate # censor private information
+          ;
       };
-    in lib.mkMerge (map (user: {
-      ${user}.packages = packages;
-    }) users);
+    in userLib.mkUserPackages config.my.toggleUsers.apps packages;
   };
 }