feat: use flake-parts to clean up the flake.nix

This is much more manageable!

flake-modules/example-vm.nix

@@ -0,0 +1,46 @@
+{ inputs, lib, ... }:
+{
+  # Example vm configuration
+  flake.nixosConfigurations.vm =
+    let
+      system = "x86_64-linux";
+      overlays = builtins.attrValues inputs.self.overlays;
+      config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [ "steam-original" ];
+      pkgs = import inputs.nixpkgs { inherit system overlays config; };
+    in
+    lib.nixosSystem {
+      inherit system pkgs;
+      modules = [
+        inputs.self.nixosModules.vm # import vm module
+        {
+          time.timeZone = "Europe/Berlin";
+          i18n.defaultLocale = "en_US.UTF-8";
+          users.users.jdoe = {
+            password = "example";
+            isNormalUser = true;
+            extraGroups = [
+              "wheel"
+              "video"
+              "networkmanager"
+            ];
+          };
+          home-manager.users.jdoe = {
+            home = {
+              username = "jdoe";
+              homeDirectory = "/home/jdoe";
+            };
+            jhome = {
+              enable = true;
+              gui.enable = true;
+              dev.rust.enable = true;
+            };
+          };
+          nix.registry.nixpkgs.flake = inputs.nixpkgs;
+          jconfig = {
+            enable = true;
+            gui.enable = true;
+          };
+        }
+      ];
+    };
+}