chore(flake): cleaner flake.nix file, update flake.lock

flake.nix

@@ -2,37 +2,35 @@
   description = "System information in JSON format for eww";
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
     rust-overlay = {
       url = "github:oxalica/rust-overlay";
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
+
   outputs = {
     nixpkgs,
     rust-overlay,
+    flake-utils,
     ...
-  }: let
-    supportedSystems = ["x86_64-linux" "aarch64-linux"];
-    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
-    pkgsFor = nixpkgs.legacyPackages;
-  in {
-    packages = forAllSystems (system: {
-      default = pkgsFor.${system}.callPackage ./. {};
-    });
-    formatter = forAllSystems (system: nixpkgs.legacyPackages.${system}.alejandra);
-    devShells = forAllSystems (
+  }:
+    flake-utils.lib.eachSystem ["x86_64-linux" "aarch64-linux"] (
       system: let
         overlays = [(import rust-overlay)];
-        pkgs = import nixpkgs {inherit system overlays;};
+        pkgs = import nixpkgs { inherit system overlays; };
         rustVersion = pkgs.rust-bin.fromRustupToolchainFile ./rustup-toolchain.toml;
-      in
-        pkgs.mkShell {
-          buildInputs = with pkgs; [
-            bacon
-            cargo
-            rustVersion
-          ];
-        }
+        pkgsFor = nixpkgs.legacyPackages;
+      in {
+        formatter = pkgs.alejandra;
+        packages.default = pkgsFor.${system}.callPackage ./. {};
+        devShells.default = with pkgs;
+          mkShell {
+            buildInputs = [
+              bacon
+              rustVersion
+            ];
+          };
+      }
     );
-  };
 }