CI: integrate with codecov

Author: Mikhail Vasilyev

.github/workflows/ci.yml

@@ -68,3 +68,22 @@ jobs:
       env:
         RUSTFLAGS: --cfg docsrs -Dwarnings
         RUSTDOCFLAGS: --cfg docsrs -Dwarnings
+
+  coverage:
+    name: Code coverage
+    runs-on: ubuntu-latest
+    needs: checks
+    steps:
+    - uses: actions/checkout@v5
+    - uses: dtolnay/rust-toolchain@stable
+    - uses: taiki-e/install-action@v2
+      with:
+        tool: nextest,cargo-llvm-cov
+    - name: Generate code coverage
+      run: cargo llvm-cov nextest --all-features --workspace --ignore-run-fail --lcov > lcov.txt
+    - name: Upload coverage report
+      uses: codecov/codecov-action@v5
+      with:
+        fail_ci_if_error: true
+        files: ./lcov.txt
+        token: ${{ secrets.CODECOV_TOKEN }}