test(api): add retry mechanism tests for ApiCall class

- Add `ApiCallRetryTest.php` with tests for exception handling scenarios
- Test retry logic for server errors, client errors, and timeout responses
- Verify 4xx errors are not retried while 5xx errors trigger retries
- Test node health check updates after failed requests
- Ensure 408 timeout errors are skipped and retrying continues

Author: tharropoulos