refactor(nix): simplify style tool outputs

flake.nix

@@ -82,40 +82,30 @@
       ...
     }@inputs:
     let
-      supportedSystems = [ "x86_64-linux" ];
-      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
-      pkgsFor = system: nixpkgs.legacyPackages.${system};
-      treefmtEvalFor = system: treefmt-nix.lib.evalModule (pkgsFor system) ./treefmt.nix;
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+      treefmtEval = treefmt-nix.lib.evalModule pkgs ./treefmt.nix;
+      nixStyleCheck = pkgs.writeShellApplication {
+        name = "nix-style-check";
+        runtimeInputs = [
+          treefmtEval.config.build.wrapper
+          pkgs.statix
+          pkgs.deadnix
+        ];
+        text = ''
+          treefmt --fail-on-change
+          statix check .
+          deadnix --fail --no-lambda-pattern-names --no-underscore .
+        '';
+      };
     in
     {
-      formatter = forAllSystems (system: (treefmtEvalFor system).config.build.wrapper);
+      formatter.${system} = treefmtEval.config.build.wrapper;
 
-      apps = forAllSystems (
-        system:
-        let
-          pkgs = pkgsFor system;
-          treefmtEval = treefmtEvalFor system;
-          nixStyleCheck = pkgs.writeShellApplication {
-            name = "nix-style-check";
-            runtimeInputs = [
-              treefmtEval.config.build.wrapper
-              pkgs.statix
-              pkgs.deadnix
-            ];
-            text = ''
-              treefmt --fail-on-change
-              statix check .
-              deadnix --fail --no-lambda-pattern-names --no-underscore .
-            '';
-          };
-        in
-        {
-          nix-style-check = {
-            type = "app";
-            program = "${nixStyleCheck}/bin/nix-style-check";
-          };
-        }
-      );
+      apps.${system}.nix-style-check = {
+        type = "app";
+        program = "${nixStyleCheck}/bin/nix-style-check";
+      };
 
       nixosConfigurations = (import ./src/dotfiles {
         inherit inputs self;