How can I manually close an `AIOEngine` or `SyncEngine` safely?

It seems that there are not method to close an Engine, the only possible way is `engine.client.close()` to close the client...But I am not sure

Begin with the AIOEngine and SyncEngine APIs referenced in the issue and inspect how their client is exposed. Confirm the supported safe shutdown behavior for each engine, then determine whether the public API or documentation needs updating. Done means both sync and async engines have an explicit, verified way to close resources, with usage guidance.

Written by the indexing model from the issue text.