Keep fixing #631
This pull request updates the crawl_tool function to return its results as a JSON string instead of a dictionary, and adjusts the unit tests accordingly to handle the new return type. The changes ensure consistent serialization of output and proper validation in tests.
* test: add more test on test_tts.py
* test: add unit test of search and retriever in tools
* test: remove the main code of search.py
* test: add the travily_search unit test
* reformate the codes
* test: add unit tests of tools
* Added the pytest-asyncio dependency
* added the license header of test_tavily_search_api_wrapper.py
