Refactor user option types across modules for consistency

Updated multiple configuration files to replace the user option type with a unified `usersOptionType`, enhancing consistency in user management across applications and services. This change simplifies the user configuration process and improves maintainability.

config/stylix.nix

@@ -17,9 +17,8 @@ in
   options.my.stylix = {
     enable = lib.mkEnableOption "system-wide theming with Stylix";
     users = lib.mkOption {
-      type = lib.types.either lib.types.str (lib.types.listOf lib.types.str);
+      type = inputs.self.lib.usersOptionType lib;
       default = config.my.toggleUsers.stylix;
-      merge = inputs.self.lib.mergeUsersOption lib;
       description = "Users to apply Stylix theming for";
     };
   };