fastlio2 保存每帧的点云和每帧的里程计为单独的文件做后端回环优化和手动回环优化

为了 提供数据做后端回环优化和手动回环优化，需要保存每帧的点云和每帧的里程计为单独的文件，并且需要保存的名字为ros时间戳。

效果很好，比我自己写的手动回环模块好用

// This is an advanced implementation of the algorithm described in the
// following paper:
//   J. Zhang and S. Singh. LOAM: Lidar Odometry and Mapping in Real-time.
//     Robotics: Science and Systems Conference (RSS). Berkeley, CA, July 2014.
 
// Modifier: Livox               dev@livoxtech.com
 
// Copyright 2013, Ji Zhang, Carnegie Mellon University
// Further contributions copyright (c) 2016, Southwest Research Institute
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice,
//    this list of c