*
 * <p>
 * The class uses synchronization to ensure thread safety when accessing and modifying the URL queue.
 * It also checks for duplicate URLs before adding them to the queue,
 * both within the queue itself and against previously accessed URLs stored in the {@link MemoryDataHelper}.
 * </p>
 *
 */
/**
 * This class is an implementation of {@link UrlQueueService}.
 */