chore(ci): build Nix flake

.github/workflows/ci.yml

@@ -67,3 +67,17 @@ jobs:
           build-type: RelWithDebInfo
           configure-options: -D CMAKE_BUILD_TYPE=RelWithDebInfo -D CMAKE_TOOLCHAIN_FILE=${{ runner.workspace }}/openspades/vcpkg/scripts/buildsystems/vcpkg.cmake -D VCPKG_TARGET_TRIPLET=x64-osx -D CMAKE_OSX_ARCHITECTURES=x86_64
           parallel: 8
+  
+  build-nix:
+    name: Build (Linux + Nix)
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v17
+
+      - name: Build Nix flake
+        run: nix build
+