Ensure @start methods emit MethodExecutionStartedEvent (#2114)

Previously, `@start` methods triggered a `FlowStartedEvent` but did not
emit a `MethodExecutionStartedEvent`. This was fine for a single entry
point but caused ambiguity when multiple `@start` methods existed.

This commit (1) emits events for starting points, (2) adds tests
ensuring ordering, (3) adds more fields to events.

src/crewai/flow/flow_events.py

@@ -1,6 +1,8 @@
 from dataclasses import dataclass, field
 from datetime import datetime
-from typing import Any, Optional
+from typing import Any, Dict, Optional, Union
+
+from pydantic import BaseModel
 
 
 @dataclass
@@ -15,17 +17,21 @@ class Event:
 
 @dataclass
 class FlowStartedEvent(Event):
-    pass
+    inputs: Optional[Dict[str, Any]] = None
 
 
 @dataclass
 class MethodExecutionStartedEvent(Event):
     method_name: str
+    state: Union[Dict[str, Any], BaseModel]
+    params: Optional[Dict[str, Any]] = None
 
 
 @dataclass
 class MethodExecutionFinishedEvent(Event):
     method_name: str
+    state: Union[Dict[str, Any], BaseModel]
+    result: Any = None
 
 
 @dataclass