CI: add reusable actions

.github/workflows/nix-build.yml

@@ -0,0 +1,37 @@
+on:
+  workflow_call:
+    secrets:
+      CACHIX_AUTH_TOKEN:
+        required: false
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        package:
+          - hyprland
+          - hyprland-nvidia
+          - xdg-desktop-portal-hyprland
+
+    runs-on: ubuntu-latest
+    steps:
+      - name: Clone repository
+        uses: actions/checkout@v3
+        with:
+          ref: ${{ github.ref }}
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v22
+        with:
+          install_url: https://nixos.org/nix/install
+          extra_nix_config: |
+            auto-optimise-store = true
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+            experimental-features = nix-command flakes
+
+      - uses: cachix/cachix-action@v12
+        with:
+          name: hyprland
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+
+      - run: nix build -L ${{ matrix.command }}