docs: public static void stop() {
          synchronized (lock) {
              if (singleton == null) return;
              LeaderSelector leaderSelector = singleton.leaderSelector;
              if (leaderSelector == null) {
                  return;
              }
              LOG.info("节点退出zk选举");
              leaderSelector.close();
              singleton = null;
              LOG.info("退出选举 完毕");
          }
      }