Fix tool propagation bug in hierarchical crews (#3679)

- Remove check_tools validator from task.py that was extending task.tools
  with agent.tools at creation time
- This caused manager agents in hierarchical crews to incorrectly inherit
  tools from task agents
- The crew.py execution logic already handles tool resolution correctly
  at execution time via fallback: task.tools or agent_to_use.tools or []
- Add reproduction test test_hierarchical_crew_does_not_propagate_agent_tools_to_manager
- Update test_task_tool_reflect_agent_tools to verify execution-time behavior

Fixes #3679

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

tests/test_task.py

@@ -20,11 +20,13 @@ from crewai.utilities.string_utils import interpolate_only
 
 
 def test_task_tool_reflect_agent_tools():
+    """Test that agent tools are available during task execution via crew fallback logic."""
     from crewai.tools import tool
 
     @tool
-    def fake_tool() -> None:
+    def fake_tool() -> str:
         "Fake tool"
+        return "result"
 
     researcher = Agent(
         role="Researcher",
@@ -40,7 +42,9 @@ def test_task_tool_reflect_agent_tools():
         agent=researcher,
     )
 
-    assert task.tools == [fake_tool]
+    assert task.tools == []
+    
+    assert researcher.tools == [fake_tool]
 
 
 def test_task_tool_takes_precedence_over_agent_tools():