Fix AttributeError when tool fields are None in OpenAI Agents SDK instrumentation

In get_response_tool_web_search_attributes() and get_response_tool_file_search_attributes(), hasattr() returns True for optional fields set to None, but accessing .__dict__ on None raises AttributeError. Added is not None guard for user_location, filters, and ranking_options fields.

Fixes #1285

Author: YouFoxGirl