Add task decomposition feature (Issue #2717)

This PR implements task decomposition as requested in Issue #2717.
It allows complex tasks to be automatically split into sub-tasks
without manual intervention.

- Added parent_task and sub_tasks fields to Task class
- Implemented decompose() method to create sub-tasks
- Added combine_sub_task_results() method to aggregate results
- Updated execute_sync() to handle sub-task execution
- Added execute_sub_tasks_async() for asynchronous execution
- Created tests for the task decomposition functionality
- Added example script demonstrating usage

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

tests/test_task_decomposition.py

@@ -0,0 +1,157 @@
+import pytest
+from unittest.mock import Mock, patch
+
+from crewai import Agent, Task
+
+
+def test_task_decomposition_structure():
+    """Test that task decomposition creates the proper parent-child relationship."""
+    agent = Agent(
+        role="Researcher",
+        goal="Research effectively",
+        backstory="You're an expert researcher",
+    )
+    
+    parent_task = Task(
+        description="Research the impact of AI on various industries",
+        expected_output="A comprehensive report",
+        agent=agent,
+    )
+    
+    sub_task_descriptions = [
+        "Research AI impact on healthcare",
+        "Research AI impact on finance",
+        "Research AI impact on education",
+    ]
+    
+    sub_tasks = parent_task.decompose(
+        descriptions=sub_task_descriptions,
+        expected_outputs=["Healthcare report", "Finance report", "Education report"],
+        names=["Healthcare", "Finance", "Education"],
+    )
+    
+    assert len(sub_tasks) == 3
+    assert len(parent_task.sub_tasks) == 3
+    
+    for sub_task in sub_tasks:
+        assert sub_task.parent_task == parent_task
+        assert parent_task in sub_task.context
+
+
+def test_task_execution_with_sub_tasks():
+    """Test that executing a task with sub-tasks executes the sub-tasks first."""
+    agent = Agent(
+        role="Researcher",
+        goal="Research effectively",
+        backstory="You're an expert researcher",
+    )
+    
+    parent_task = Task(
+        description="Research the impact of AI on various industries",
+        expected_output="A comprehensive report",
+        agent=agent,
+    )
+    
+    sub_task_descriptions = [
+        "Research AI impact on healthcare",
+        "Research AI impact on finance",
+        "Research AI impact on education",
+    ]
+    
+    parent_task.decompose(
+        descriptions=sub_task_descriptions,
+        expected_outputs=["Healthcare report", "Finance report", "Education report"],
+    )
+    
+    with patch.object(Agent, 'execute_task', return_value="Mock result") as mock_execute_task:
+        result = parent_task.execute_sync()
+        
+        assert mock_execute_task.call_count >= 3
+        
+        for sub_task in parent_task.sub_tasks:
+            assert sub_task.output is not None
+        
+        assert result is not None
+        assert result.raw is not None
+
+
+def test_combine_sub_task_results():
+    """Test that combining sub-task results works correctly."""
+    agent = Agent(
+        role="Researcher",
+        goal="Research effectively",
+        backstory="You're an expert researcher",
+    )
+    
+    parent_task = Task(
+        description="Research the impact of AI on various industries",
+        expected_output="A comprehensive report",
+        agent=agent,
+    )
+    
+    sub_tasks = parent_task.decompose([
+        "Research AI impact on healthcare",
+        "Research AI impact on finance",
+    ])
+    
+    for sub_task in sub_tasks:
+        sub_task.output = Mock()
+        sub_task.output.raw = f"Result for {sub_task.description}"
+    
+    with patch.object(Agent, 'execute_task', return_value="Combined result") as mock_execute_task:
+        result = parent_task.combine_sub_task_results()
+        
+        assert mock_execute_task.called
+        assert result == "Combined result"
+
+
+def test_task_decomposition_validation():
+    """Test that task decomposition validates inputs correctly."""
+    parent_task = Task(
+        description="Research the impact of AI",
+        expected_output="A report",
+    )
+    
+    with pytest.raises(ValueError, match="At least one sub-task description is required"):
+        parent_task.decompose([])
+    
+    with pytest.raises(ValueError, match="expected_outputs must have the same length"):
+        parent_task.decompose(
+            ["Task 1", "Task 2"], 
+            expected_outputs=["Output 1"]
+        )
+    
+    with pytest.raises(ValueError, match="names must have the same length"):
+        parent_task.decompose(
+            ["Task 1", "Task 2"], 
+            names=["Name 1"]
+        )
+
+
+def test_execute_sub_tasks_async():
+    """Test that executing sub-tasks asynchronously works correctly."""
+    agent = Agent(
+        role="Researcher",
+        goal="Research effectively",
+        backstory="You're an expert researcher",
+    )
+    
+    parent_task = Task(
+        description="Research the impact of AI on various industries",
+        expected_output="A comprehensive report",
+        agent=agent,
+    )
+    
+    sub_tasks = parent_task.decompose([
+        "Research AI impact on healthcare",
+        "Research AI impact on finance",
+    ])
+    
+    with patch.object(Task, 'execute_async') as mock_execute_async:
+        mock_future = Mock()
+        mock_execute_async.return_value = mock_future
+        
+        futures = parent_task.execute_sub_tasks_async()
+        
+        assert mock_execute_async.call_count == 2
+        assert len(futures) == 2