feat: add nix ci workflow

.github/workflows/ci-nix.yml

@@ -0,0 +1,21 @@
+name: Nix CI
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: Run Flake Check
+        run: nix flake check
+
+      - name: Run a Build
+        run: nix build .#default
+