Update documentation to cover testing using pytest

Please add a section in your documentation on how to test code that uses pool, fetch, executemany etc using pytest. I could not find anything on stackoverflow or issues where is a slight reference somewhere to TempCluster but no examples whatsoever. Are you supposed to mock this library or create an actual database while testing. Would be super helpful for future readers

首先查看现有文档以及 issue 中提到的简要 TempCluster 参考。添加用于测试 pool、fetch 和 executemany 用法的 pytest 指导和示例，包括文档中说明的在使用 mocking 和使用实际数据库之间的选择。