Fix duplicate tool execution in structured_tool.invoke()

- Remove duplicate function call on line 285 that caused tools to execute twice
- Add comprehensive test to prevent regression
- Fixes issue #3489

Co-Authored-By: João <joao@crewai.com>

src/crewai/tools/structured_tool.py

@@ -282,8 +282,6 @@ class CrewStructuredTool:
         except Exception:
             raise
 
-        result = self.func(**parsed_args, **kwargs)
-
         if asyncio.iscoroutine(result):
             return asyncio.run(result)