set up treefmt action

.github/workflows/treefmt.yml

@@ -0,0 +1,15 @@
+name: build_systems
+on:
+  workflow_dispatch:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    name: nix fmt
+    runs-on: self-hosted
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build default package
+        run: "treefmt --ci"