ci: add a cargo-llvm-cov coverage job

.github/workflows/ci.yml

@@ -41,3 +41,34 @@ jobs:
 
       - name: Build release
         run: cargo build --release
+
+  coverage:
+    runs-on: ubuntu-latest
+    container: archlinux:latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: System dependencies
+        run: |
+          pacman -Syu --noconfirm --needed \
+            base-devel \
+            gtk4 libadwaita glib2 \
+            pkgconf
+
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy, llvm-tools-preview
+
+      - uses: taiki-e/install-action@cargo-llvm-cov
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Generate coverage
+        run: cargo llvm-cov --lcov --output-path lcov.info
+
+      - name: Upload coverage artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: lcov-info
+          path: lcov.info
+          if-no-files-found: error