Thread safety of client-v2 Client

Documentation for client-v2 never explicitly states that Client class is thread-safe or not. From code it appears to be thread-safe, but it would be very useful to have an official confirmation on whether the same Client object can be reused across threads or it should be created per thread.

首先查看 client-v2 Client 的文档和实现，以确定一个 Client 对象是否可以在线程之间复用。记录关于线程安全的官方指导，包括调用方应该共享一个 Client，还是为每个线程创建一个 Client；该 issue 未指定具体的文档文件或测试。

由索引模型根据 Issue 内容生成。