treefmt: upgrade nixfmt options

docs/nix/flake-module.nix

@@ -38,7 +38,7 @@
             patchShebangs --build $out
 
             ruff format --check --diff $out
-            ruff --line-length 88 $out
+            ruff check --line-length 88 $out
             mypy --strict $out
           '';
 

formatter.nix

@@ -8,43 +8,19 @@
       treefmt.programs.shellcheck.enable = true;
 
       treefmt.programs.mypy.enable = true;
+      treefmt.programs.nixfmt.enable = true;
+      treefmt.programs.nixfmt.package = pkgs.nixfmt-rfc-style;
+      treefmt.programs.deadnix.enable = true;
+
       treefmt.programs.mypy.directories = {
         "pkgs/clan-cli".extraPythonPackages = self'.packages.clan-cli.testDependencies;
         "pkgs/clan-app".extraPythonPackages =
           # clan-app currently only exists on linux
           (self'.packages.clan-app.externalTestDeps or [ ]) ++ self'.packages.clan-cli.testDependencies;
       };
+      treefmt.programs.ruff.check = true;
+      treefmt.programs.ruff.format = true;
 
-      treefmt.settings.formatter.nix = {
-        command = "sh";
-        options = [
-          "-eucx"
-          ''
-            # First deadnix
-            ${lib.getExe pkgs.deadnix} --edit "$@"
-            # Then nixpkgs-fmt
-            ${lib.getExe pkgs.nixfmt-rfc-style} "$@"
-          ''
-          "--" # this argument is ignored by bash
-        ];
-        includes = [ "*.nix" ];
-        excludes = [
-          # Was copied from nixpkgs. Keep diff minimal to simplify upstreaming.
-          "pkgs/builders/script-writers.nix"
-        ];
-      };
-      treefmt.settings.formatter.python = {
-        command = "sh";
-        options = [
-          "-eucx"
-          ''
-            ${lib.getExe pkgs.ruff} check --fix "$@"
-            ${lib.getExe pkgs.ruff} format "$@"
-          ''
-          "--" # this argument is ignored by bash
-        ];
-        includes = [ "*.py" ];
-      };
       # FIXME: currently broken in CI
       #treefmt.settings.formatter.vale =
       #  let