Stop importing nixpkgs in the flake

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1701718080,
-        "narHash": "sha256-6ovz0pG76dE0P170pmmZex1wWcQoeiomUZGggfH9XPs=",
+        "lastModified": 1712963716,
+        "narHash": "sha256-WKm9CvgCldeIVvRz87iOMi8CFVB1apJlkUT4GGvA0iM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "2c7f3c0fb7c08a0814627611d9d7d45ab6d75335",
+        "rev": "cfd6b5fc90b15709b780a5a1619695a88505a176",
         "type": "github"
       },
       "original": {

flake.nix

@@ -8,16 +8,14 @@
     nixpkgs,
   }: let
     inherit (nixpkgs) lib;
-    genSystems = lib.genAttrs [
+    forSystems = f:
+      lib.genAttrs [
         "x86_64-linux"
         "aarch64-linux"
-    ];
-    pkgsFor = system: import nixpkgs {inherit system;};
-  in {
-    devShells = genSystems (
-      system: let
-        pkgs = pkgsFor system;
+      ] (system: f nixpkgs.legacyPackages.${system});
   in {
+    devShells = forSystems (
+      pkgs: {
         default = pkgs.mkShell {
           nativeBuildInputs = [
             pkgs.clang-tools
@@ -46,6 +44,6 @@
       }
     );
 
-    formatter = genSystems (system: (pkgsFor system).alejandra);
+    formatter = forSystems (pkgs: pkgs.alejandra);
   };
 }