Update get_local_search_engine and get_global_search_engine return annotation

[longyunfeigu]

Description

get_global_search_engine and get_local_search_engine from an object-oriented perspective should return the abstract class BaseSearch rather than the concrete class: LocalSearch or GlobalSearch, with the outer layer calling the asearch method of the abstract class

Related Issues

[Reference any related issues or tasks that this pull request addresses.]

Proposed Changes

[List the specific changes made in this pull request.]

Checklist

• [x] I have tested these changes locally.
• [x] I have reviewed the code changes.
• [ ] I have updated the documentation (if necessary).
• [ ] I have added appropriate unit tests (if applicable).

Additional Notes

[Add any additional notes or context that may be helpful for the reviewer(s).]