refactor(flake): use flake-parts

This makes it easier to split up the flake in the future.

flake.lock

@@ -1,5 +1,25 @@
 {
   "nodes": {
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1727826117,
+        "narHash": "sha256-K5ZLCyfO/Zj9mPFldf3iwS6oZStJcU4tSpiXTMYaaL0=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "3d04084d54bedc3d6b8b736c70ef449225c361b1",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1727348695,
@@ -17,6 +37,7 @@
     },
     "root": {
       "inputs": {
+        "flake-parts": "flake-parts",
         "nixpkgs": "nixpkgs",
         "systems": "systems"
       }

flake.nix

@@ -3,49 +3,26 @@
   inputs = {
     nixpkgs.url = "nixpkgs/nixos-unstable";
     systems.url = "github:nix-systems/default";
+    flake-parts = {
+      url = "github:hercules-ci/flake-parts";
+      inputs.nixpkgs-lib.follows = "nixpkgs";
+    };
   };
 
   outputs =
+    inputs:
+    inputs.flake-parts.mkFlake {
+      systems = import inputs.system;
+      perSystem =
         {
-      self,
-      nixpkgs,
-      systems,
+          lib,
+          pkgs,
+          self',
+          ...
         }:
-    let
-      forEachSupportedSystem = nixpkgs.lib.genAttrs (import systems);
-    in
         {
-      checks = forEachSupportedSystem (
-        system:
+          packages =
             let
-          pkgs = nixpkgs.legacyPackages.${system};
-          inherit (nixpkgs) lib;
-        in
-        {
-          fmtRust = pkgs.callPackage ./run-cmd.nix {
-            src = self;
-            name = "fmt-rust";
-            extraNativeBuildInputs = [ pkgs.rustfmt ];
-            cmd = "${lib.getExe pkgs.cargo} fmt --all --check --verbose";
-          };
-          fmtNix = pkgs.callPackage ./run-cmd.nix {
-            src = self;
-            name = "fmt-nix";
-            cmd = "${lib.getExe self.formatter.${system}} --check .";
-          };
-          lintNix = pkgs.callPackage ./run-cmd.nix {
-            src = self;
-            name = "lint-nix";
-            cmd = "${lib.getExe pkgs.statix} check .";
-          };
-        }
-      );
-      formatter = forEachSupportedSystem (system: nixpkgs.legacyPackages.${system}.nixfmt-rfc-style);
-
-      packages = forEachSupportedSystem (
-        system:
-        let
-          pkgs = nixpkgs.legacyPackages.${system};
               webnsupdate = pkgs.callPackage ./default.nix { };
             in
             {
@@ -61,27 +38,42 @@
                   CARGO_TERM_COLOR=never cargo update 2>&1 | sed '/crates.io index/d' | tee -a cargo_update.log
                 '';
               };
-        }
-      );
+            };
 
-      overlays.default = final: prev: { webnsupdate = final.callPackage ./default.nix { }; };
+          formatter = pkgs.nixfmt-rfc-style;
 
-      nixosModules.default = ./module.nix;
+          checks = {
+            fmtRust = pkgs.callPackage ./run-cmd.nix {
+              src = inputs.self;
+              name = "fmt-rust";
+              extraNativeBuildInputs = [ pkgs.rustfmt ];
+              cmd = "${lib.getExe pkgs.cargo} fmt --all --check --verbose";
+            };
+            fmtNix = pkgs.callPackage ./run-cmd.nix {
+              src = inputs.self;
+              name = "fmt-nix";
+              cmd = "${lib.getExe self'.formatter} --check .";
+            };
+            lintNix = pkgs.callPackage ./run-cmd.nix {
+              src = inputs.self;
+              name = "lint-nix";
+              cmd = "${lib.getExe pkgs.statix} check .";
+            };
+          };
 
-      devShells = forEachSupportedSystem (
-        system:
-        let
-          pkgs = nixpkgs.legacyPackages.${system};
-        in
-        {
-          default = pkgs.mkShell {
+          devShells.default = pkgs.mkShell {
             packages = [
               pkgs.cargo-insta
               pkgs.cargo-udeps
               pkgs.mold
             ];
           };
-        }
-      );
+        };
+
+      flake = {
+        overlays.default = final: prev: { webnsupdate = final.callPackage ./default.nix { }; };
+
+        nixosModules.default = ./module.nix;
+      };
     };
 }