add llvm-cov to template ci

Author: joshrotenberg

template/.github/workflows/ci.yml

@@ -62,3 +62,23 @@ jobs:
           RUSTDOCFLAGS: -D warnings
         run: cargo doc --no-deps --document-private-items --all-features --workspace --examples
 {% endraw  %}
+
+  coverage:
+    name: Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+      - name: Generate code coverage
+        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }} 
+          files: lcov.info
+          fail_ci_if_error: true