add github workflow

.github/workflows/build.yaml

@@ -0,0 +1,32 @@
+name: Build
+on: push
+
+jobs:
+  build:
+    runs-on: "ubuntu-22.04"
+
+    steps:
+      -uses: actions/checkout@v4
+
+      - uses: cachix/install-nix-action@v24
+
+      - uses: cachix/cachix-action@v13
+        with:
+          name: mlabs
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+
+      - name: Build GDExtension for Windows
+        run: nix build .#libcsl_godot-win
+
+      - uses: actions/upload-artifact@v4
+        path: result/bin/csl_godot.dll
+        with:
+          name: libcsl_godot-win
+
+      - name: Build Demo app for Windows
+        run: nix build .#csl_demo-win
+
+      - uses: actions/upload-artifact@v4
+        path: result/bin/
+        with:
+          name: csl_demo-win