refactor(nix): migrate from flake-utils to flake-parts (#250)

* fix(ci): move install to nix action

* refactor(nix): migrate from flake-utils to flake-parts

Replace flake-utils with flake-parts for a more modular and type-safe
Nix flake configuration. flake-parts uses the NixOS module system
pattern, providing better extensibility and composability.

Key changes:
- Replace flake-utils input with flake-parts
- Use mkFlake with perSystem pattern instead of eachDefaultSystem
- Explicitly declare supported systems (x86_64-linux, aarch64-linux,
  aarch64-darwin)
- Remove x86_64-darwin from supported systems as it is no longer needed

Benefits of flake-parts:
- NixOS-style module system for flake configuration
- Type-safe options with better error messages
- Support for advanced features like partitions and flakeModules
- More maintainable structure for complex flake configurations

* feat(nix): add nixfmt-rfc-style to dev dependencies and lefthook

Add nixfmt-rfc-style as a development dependency in the Nix flake and
configure lefthook to automatically format .nix files on pre-commit.

Uses `nix develop --command` to run nixfmt from the devShell context,
ensuring consistent Nix code formatting across the project.

Author: ryoppippi

flake.lock

@@ -3,30 +3,37 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
-    flake-utils.url = "github:numtide/flake-utils";
+    flake-parts.url = "github:hercules-ci/flake-parts";
   };
 
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (system:
-      let
-        pkgs = nixpkgs.legacyPackages.${system};
-      in
-      {
-        devShells.default = pkgs.mkShell {
-          buildInputs = with pkgs; [
-            pnpm_10
-          ];
+  outputs =
+    inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "aarch64-darwin"
+      ];
 
-          shellHook = ''
-            echo "StackOne AI Node SDK development environment"
+      perSystem =
+        { pkgs, ... }:
+        {
+          devShells.default = pkgs.mkShell {
+            buildInputs = with pkgs; [
+              pnpm_10
+              nixfmt-rfc-style
+            ];
 
-            # Install dependencies only if node_modules/.pnpm/lock.yaml is older than pnpm-lock.yaml
-            if [ ! -f node_modules/.pnpm/lock.yaml ] || [ pnpm-lock.yaml -nt node_modules/.pnpm/lock.yaml ]; then
-              echo "📦 Installing dependencies..."
-              pnpm install --frozen-lockfile
-            fi
-          '';
+            shellHook = ''
+              echo "StackOne AI Node SDK development environment"
+
+              # Install dependencies only if node_modules/.pnpm/lock.yaml is older than pnpm-lock.yaml
+              if [ ! -f node_modules/.pnpm/lock.yaml ] || [ pnpm-lock.yaml -nt node_modules/.pnpm/lock.yaml ]; then
+                echo "📦 Installing dependencies..."
+                pnpm install --frozen-lockfile
+              fi
+            '';
+          };
         };
-      }
-    );
+    };
 }

flake.nix

@@ -9,6 +9,10 @@ pre-commit:
       glob: '*'
       run: pnpm oxfmt --no-error-on-unmatched-pattern {staged_files}
       stage_fixed: true
+    - name: nixfmt
+      glob: '*.nix'
+      run: nix develop --command nixfmt {staged_files}
+      stage_fixed: true
 
 pre-push:
   jobs: