refactor: Move events module to crewai.events (#3425)

refactor(events): relocate events module & update imports

- Move events from utilities/ to top-level events/ with types/, listeners/, utils/ structure
- Update all source/tests/docs to new import paths
- Add backwards compatibility stubs in crewai.utilities.events with deprecation warnings
- Restore test mocks and fix related test imports

src/crewai/events/__init__.py

@@ -0,0 +1,56 @@
+"""CrewAI events system for monitoring and extending agent behavior.
+
+This module provides the event infrastructure that allows users to:
+- Monitor agent, task, and crew execution
+- Track memory operations and performance
+- Build custom logging and analytics
+- Extend CrewAI with custom event handlers
+"""
+
+from crewai.events.base_event_listener import BaseEventListener
+from crewai.events.event_bus import crewai_event_bus
+
+from crewai.events.types.memory_events import (
+    MemoryQueryCompletedEvent,
+    MemorySaveCompletedEvent,
+    MemorySaveStartedEvent,
+    MemoryQueryStartedEvent,
+    MemoryRetrievalCompletedEvent,
+    MemorySaveFailedEvent,
+    MemoryQueryFailedEvent,
+)
+
+from crewai.events.types.knowledge_events import (
+    KnowledgeRetrievalStartedEvent,
+    KnowledgeRetrievalCompletedEvent,
+)
+
+from crewai.events.types.crew_events import (
+    CrewKickoffStartedEvent,
+    CrewKickoffCompletedEvent,
+)
+from crewai.events.types.agent_events import (
+    AgentExecutionCompletedEvent,
+)
+
+from crewai.events.types.llm_events import (
+    LLMStreamChunkEvent,
+)
+
+__all__ = [
+    "BaseEventListener",
+    "crewai_event_bus",
+    "MemoryQueryCompletedEvent",
+    "MemorySaveCompletedEvent",
+    "MemorySaveStartedEvent",
+    "MemoryQueryStartedEvent",
+    "MemoryRetrievalCompletedEvent",
+    "MemorySaveFailedEvent",
+    "MemoryQueryFailedEvent",
+    "KnowledgeRetrievalStartedEvent",
+    "KnowledgeRetrievalCompletedEvent",
+    "CrewKickoffStartedEvent",
+    "CrewKickoffCompletedEvent",
+    "AgentExecutionCompletedEvent",
+    "LLMStreamChunkEvent",
+]