ci: add nix ci

.github/workflows/nix.yml

@@ -0,0 +1,32 @@
+name: Continuous Integration (Nix)
+
+on:
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+  pull_request:
+  merge_group:
+
+# ensure that the workflow is only triggered once per PR,  subsequent pushes to the PR will cancel
+# and restart the workflow. See https://docs.github.com/en/actions/using-jobs/using-concurrency
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: docker/setup-qemu-action@v3
+    - uses: cachix/install-nix-action@v27
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+    - uses: DeterminateSystems/magic-nix-cache-action@v2
+    # Build and test tracexec
+    # Also builds kernels
+    - run: nix build
+    # Run Userspace<->Kernel CI
+    - run: nix run '.#ukci'