workflows: add nix-test workflow

Checks the flake
Builds and tests the package

.github/workflows/nix-tests.yml

@@ -0,0 +1,17 @@
+name: "Nix-Tests"
+on:
+  pull_request:
+  push:
+jobs:
+  nix-flake-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v27
+      with:
+        extra_nix_config: |
+          experimental-features = nix-command flakes
+          access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+    - run: nix flake show
+    - run: nix flake check --print-build-logs
+    - run: nix build --print-build-logs