ci: add coverage reporting job to GitHub Actions workflow

- Add dedicated coverage job that runs tests with text and LCOV reporters
- Upload LCOV coverage reports to Codecov for tracking and badge generation
- Run on Ubuntu latest for consistent coverage metrics
- Complements existing build and lint jobs in CI pipeline

Signed-off-by: leocavalcante <leo@cavalcante.dev>

Author: leocavalcante

.github/workflows/ci.yml

@@ -45,3 +45,26 @@ jobs:
 
       - name: Check formatting and lint
         run: bunx biome check src/ tests/
+
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Install dependencies
+        run: bun install
+
+      - name: Generate coverage report
+        run: bun test --coverage --coverage-reporter=text --coverage-reporter=lcov
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          files: ./coverage/lcov.info
+          flags: unittests
+          name: codecov-umbrella