fix: update nixfmt workflow to use 'main' branch and improve formatting checks

.github/workflows/nixfmt.yml

@@ -3,7 +3,7 @@ name: Nix Format Check
 on:
   pull_request:
   push:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   check-format:
@@ -13,17 +13,32 @@ jobs:
       
       - name: Install Nix
         uses: cachix/install-nix-action@v30
-        
+        with:
+          extra_nix_config: |
+            experimental-features = nix-command flakes
+
       - name: Install nixfmt
-        run: nix-env -i nixfmt-rfc-style
+        run: nix profile install nixpkgs#nixfmt-rfc-style
         
       - name: Check Nix formatting
         run: |
-          find . -name "*.nix" -type f -exec nixfmt {} \;
-          if git diff --quiet; then
-            echo "All Nix files are properly formatted"
+          exit_code=0
+          while IFS= read -r file; do
+            if ! nixfmt "$file"; then
+              echo "Error: Failed to format $file"
+              exit_code=1
+              break
+            fi
+          done < <(find . -name "*.nix" -type f)
+          
+          if [ $exit_code -eq 0 ]; then
+            if git diff --quiet; then
+              echo "All Nix files are properly formatted"
+            else
+              echo "Error: Some Nix files are not properly formatted"
+              git diff
+              exit 1
+            fi
           else
-            echo "Error: Some Nix files are not properly formatted"
-            git diff
-            exit 1
-          fi
+            exit $exit_code
+          fi