move flake-parts into pkgs or toplevel

formatter.nix

@@ -0,0 +1,41 @@
+{ lib
+, inputs
+, ...
+}: {
+  imports = [
+    inputs.treefmt-nix.flakeModule
+  ];
+  perSystem = { pkgs, ... }: {
+    treefmt.projectRootFile = "flake.nix";
+    treefmt.flakeCheck = true;
+    treefmt.flakeFormatter = true;
+    treefmt.programs.shellcheck.enable = true;
+    treefmt.settings.formatter.nix = {
+      command = "sh";
+      options = [
+        "-eucx"
+        ''
+          # First deadnix
+          ${lib.getExe pkgs.deadnix} --edit "$@"
+          # Then nixpkgs-fmt
+          ${lib.getExe pkgs.nixpkgs-fmt} "$@"
+        ''
+        "--" # this argument is ignored by bash
+      ];
+      includes = [ "*.nix" ];
+    };
+    treefmt.settings.formatter.python = {
+      command = "sh";
+      options = [
+        "-eucx"
+        ''
+          ${lib.getExe pkgs.ruff} --fix "$@"
+          ${lib.getExe pkgs.black} "$@"
+        ''
+        "--" # this argument is ignored by bash
+      ];
+      includes = [ "*.py" ];
+    };
+  };
+}
+