Refactor event handling and introduce new event types

- Migrate from global `emit` function to `event_bus.emit`
- Add new event types for task failures, tool usage, and agent execution
- Update event listeners and event bus to support more granular event tracking
- Remove deprecated event emission methods
- Improve event type consistency and add more detailed event information

src/crewai/utilities/events/task_events.py

@@ -20,3 +20,11 @@ class TaskCompleted(CrewEvent):
     type: str = "task_completed"
 
     model_config = {"arbitrary_types_allowed": True}
+
+
+class TaskFailed(CrewEvent):
+    """Event emitted when a task fails"""
+
+    task: Any
+    error: str
+    type: str = "task_failed"