add coverage GH actions workflow

.github/workflows/coverage.yaml

@@ -0,0 +1,47 @@
+name: Coverage
+
+on:
+  push:
+    branches:
+      - master
+      - coverage
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  codecov:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup rust toolchain
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          toolchain: stable
+          components: llvm-tools-preview
+
+      - name: Run tests
+        env:
+          RUSTFLAGS: "-Cinstrument-coverage"
+          RUSTDOCFLAGS: "-Cinstrument-coverage"
+        run: cargo test
+
+      - name: Install grcov
+        run: cargo install grcov
+
+      - name: Generate coverage report
+        run: >
+          grcov . -s . --binary-path target/debug/ -t lcov --branch
+          --ignore-not-existing -o coverage.lcov
+
+      - name: Upload coverage report
+        uses: codecov/codecov-action@v4
+        with:
+          fail_ci_if_error: true
+          file: coverage.lcov
+          flags: rust
+          token: ${{ secrets.CODECOV_TOKEN }}
+