Refactor user management functions to use inputs

Removed the `lib.nix` file and refactored various modules to utilize `inputs.self.lib` for user package and attribute management. This change enhances consistency and maintainability across the configuration files.

modules/shell/exercism.nix

@@ -1,5 +1,6 @@
 {
   config,
+  inputs,
   lib,
   pkgs,
   ...
@@ -8,13 +9,12 @@
   options.my.shell.exercism.enable = lib.mkEnableOption "Exercism coding practice platform";
   config = lib.mkIf config.my.shell.exercism.enable {
     users.users = let
-      userLib = import ../lib.nix { inherit lib; };
       packages = builtins.attrValues {
         inherit (pkgs)
           exercism # learn to code
           bats # testing system, required by Exercism
           ;
       };
-    in userLib.mkUserPackages config.my.toggleUsers.shell packages;
+    in inputs.self.lib.mkUserPackages lib config.my.toggleUsers.shell packages;
   };
 }