Add Datadog code coverage upload alongside Codecov

Side-by-side coverage reporting: adds Datadog coverage upload step
after the existing Codecov upload in the coverage workflow. Uses the
DataDog/coverage-upload-github-action with LCOV format. Both systems
will run in parallel for comparison.

Author: ManuelPalenzuelaDD

.github/workflows/coverage.yml

@@ -50,3 +50,11 @@ jobs:
           token: ${{ secrets.CODECOV_TOKEN }}
           files: lcov.info
           fail_ci_if_error: true
+      - name: Upload coverage to Datadog
+        if: always()
+        continue-on-error: true
+        uses: DataDog/coverage-upload-github-action@v1
+        with:
+          api_key: ${{ secrets.DATADOG_API_KEY }}
+          files: lcov.info
+          format: lcov