fix: upgrade codecov action to v4 and add token support

- Upgrade from codecov/codecov-action@v3 to @v4 for better reliability
- Add token parameter to resolve rate limiting issues
- Requires CODECOV_TOKEN secret to be configured in repository settings

Author: rschumann

.github/workflows/ci.yml

@@ -50,9 +50,10 @@ jobs:
         REDIS_URL: redis://localhost:6379/0
 
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
       with:
         file: ./coverage/lcov.info
+        token: ${{ secrets.CODECOV_TOKEN }}
         fail_ci_if_error: true
 
   security: