feat: simplify flake.nix, correct package derivation

flake.nix

@@ -1,61 +1,38 @@
 {
   description = "System information in JSON format for eww";
-
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
-    flake-utils = {
-      url = "github:numtide/flake-utils";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
     rust-overlay = {
       url = "github:oxalica/rust-overlay";
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
-
-  outputs =
-    {
-      self,
-      nixpkgs,
-      flake-utils,
-      rust-overlay,
-    }:
-    flake-utils.lib.eachSystem [ "x86_64-linux" ] (
-      system:
-      let
-        overlays = [ (import rust-overlay) ];
-        pkgs = import nixpkgs { inherit system overlays; };
-        rustVersion = (pkgs.rust-bin.fromRustupToolchainFile ./rustup-toolchain.toml);
-        rustPlatform = pkgs.makeRustPlatform {
-          cargo = rustVersion;
-          rustc = rustVersion;
-        };
-        appName = "pumo-system-info";
-        appRustBuild = rustPlatform.buildRustPackage {
-          pname = appName;
-          version = "0.1.0";
-          src = ./.;
-          cargoLock.lockFile = ./Cargo.lock;
-          doCheck = true;
-        };
+  outputs = {
+    nixpkgs,
+    rust-overlay,
+    ...
+  }: 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 (
+      system: let
+        overlays = [(import rust-overlay)];
+        pkgs = import nixpkgs {inherit system overlays;};
+        rustVersion = pkgs.rust-bin.fromRustupToolchainFile ./rustup-toolchain.toml;
       in
-      {
-        packages.pumoSystemInfo = appRustBuild;
-        formatter = nixpkgs.legacyPackages.${system}.nixfmt-rfc-style;
-        defaultPackage = appRustBuild;
-        devShell =
-          with pkgs;
-          mkShell {
-            buildInputs = [
-              bacon
-              cargo
-              cargo-deny
-              cargo-msrv
-              cargo-tarpaulin
-              just
-              rustVersion
-            ];
-          };
-      }
+        pkgs.mkShell {
+          buildInputs = with pkgs; [
+            bacon
+            cargo
+            rustVersion
+          ];
+        }
     );
+  };
 }