refactor: move max into dentritic pattern

modules/common/features/pkgs-unstable.nix

@@ -0,0 +1,11 @@
+{ inputs, ... }: {
+  flake.nixosModules.commonUnstablePkgsOverlay = { ... }: {
+    nixpkgs.overlays = [
+      (final: prev: {
+        pkgs-unstable = import inputs.nixpkgs-unstable {
+          inherit (prev.stdenv.hostPlatform) system;
+        };
+      })
+    ];
+  };
+}