Refactor flake structure with flake-parts

flake/perSystem.nix

@@ -0,0 +1,35 @@
+{inputs, ...}: let
+  rootPath = ./..;
+in {
+  imports = [
+    (rootPath + "/treefmt.nix")
+  ];
+  perSystem = {
+    pkgs,
+    system,
+    lib,
+    self',
+    ...
+  }: let
+    inherit (inputs) nixpkgs;
+    callPackages = lib.callPackagesWith (pkgs // {inherit callPackages inputs rootPath;});
+  in {
+    _module.args.pkgs = import nixpkgs {
+      inherit system;
+      config = {
+        allowUnfree = true;
+      };
+    };
+    devShells.default = pkgs.mkShell {
+      packages = with pkgs; [
+        nixd
+        typos
+        typos-lsp
+        just
+        nvfetcher
+      ];
+    };
+    packages = callPackages (rootPath + "/pkgs") {};
+    checks = self'.packages;
+  };
+}