Refactor flake.nix and NixOS module for lidarr-mb-gap

- Updated `flake.nix` to simplify package and app definitions by using `inherit` for better readability.
- Removed the `EXAMPLE_CONFIG.nix` file to streamline the project structure, as it was no longer needed.
- Enhanced `nixos/lidarr-mb-gap.nix` to improve the import process for the source configuration, ensuring clarity and maintainability.

flake.nix

@@ -8,7 +8,7 @@
     let
       system = "x86_64-linux";
       pkgs = import nixpkgs { inherit system; };
-      lib = pkgs.lib;
+      inherit (pkgs) lib;
       lidarr-mb-gap = import ./nix/package.nix {
         inherit pkgs;
         src = lib.cleanSource ./src;
@@ -19,7 +19,7 @@
 
       packages.${system} = {
         default = lidarr-mb-gap;
-        lidarr-mb-gap = lidarr-mb-gap;
+        inherit lidarr-mb-gap;
       };
 
       apps.${system} = {