Add Codecov test results upload step

Add step to upload test results to Codecov in CI workflow.

Author: doublegate

.github/workflows/ci.yml

@@ -170,6 +170,12 @@ jobs:
       # Release artifacts are built in the dedicated release.yml workflow.
       # CI purpose is testing (debug builds sufficient for test validation).
 
+      - name: Upload test results to Codecov
+        if: ${{ !cancelled() }}
+        uses: codecov/test-results-action@v1
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+
   # Job 4: Security audit
   security_audit:
     name: Security Audit