同步时是否支持事务

以mysql2mysql为例
写入时，是否支持事务
文档中讲到pre、导入、post三者不支持同一事务，那单导入这一块是否支持同一事务？没有pre和post操作

Start with the mysql2mysql documentation and import path, focusing on the transaction behavior described for pre, import, and post. Verify whether an import-only operation uses one transaction, then update the documentation to state the behavior clearly and support the conclusion with the relevant existing tests or reproducible behavior.

Written by the indexing model from the issue text.