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/base_events.py

@@ -0,0 +1,46 @@
+from datetime import datetime, timezone
+from typing import Any, Dict, Optional
+from pydantic import BaseModel, Field
+
+from crewai.utilities.serialization import to_serializable
+
+
+class BaseEvent(BaseModel):
+    """Base class for all events"""
+
+    timestamp: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+    type: str
+    source_fingerprint: Optional[str] = None  # UUID string of the source entity
+    source_type: Optional[str] = (
+        None  # "agent", "task", "crew", "memory", "entity_memory", "short_term_memory", "long_term_memory", "external_memory"
+    )
+    fingerprint_metadata: Optional[Dict[str, Any]] = None  # Any relevant metadata
+
+    def to_json(self, exclude: set[str] | None = None):
+        """
+        Converts the event to a JSON-serializable dictionary.
+
+        Args:
+            exclude (set[str], optional): Set of keys to exclude from the result. Defaults to None.
+
+        Returns:
+            dict: A JSON-serializable dictionary.
+        """
+        return to_serializable(self, exclude=exclude)
+
+    def _set_task_params(self, data: Dict[str, Any]):
+        if "from_task" in data and (task := data["from_task"]):
+            self.task_id = task.id
+            self.task_name = task.name or task.description
+            self.from_task = None
+
+    def _set_agent_params(self, data: Dict[str, Any]):
+        task = data.get("from_task", None)
+        agent = task.agent if task else data.get("from_agent", None)
+
+        if not agent:
+            return
+
+        self.agent_id = agent.id
+        self.agent_role = agent.role
+        self.from_agent = None