feat: add started_event_id and set in eventbus

* feat: add started_event_id and set in eventbus

* chore: update additional test assumption

* fix: restore event bus handlers on context exit

fix rollback in crewai events bus so that exiting the context restores
the previous _sync_handlers, _async_handlers, _handler_dependencies, and _execution_plan_cache by assigning shallow copies of the saved dicts. previously these
were set to empty dicts on exit, which caused registered handlers and cached execution plans to be lost.

lib/crewai/tests/memory/test_external_memory.py

@@ -308,6 +308,7 @@ def test_external_memory_search_events(
         "parent_event_id": None,
         "previous_event_id": ANY,
         "triggered_by_event_id": None,
+        "started_event_id": ANY,
         "emission_sequence": ANY,
         "query": "test value",
         "limit": 3,
@@ -330,6 +331,7 @@ def test_external_memory_search_events(
         "parent_event_id": ANY,
         "previous_event_id": ANY,
         "triggered_by_event_id": None,
+        "started_event_id": ANY,
         "emission_sequence": ANY,
         "query": "test value",
         "results": [],
@@ -390,6 +392,7 @@ def test_external_memory_save_events(
         "parent_event_id": None,
         "previous_event_id": ANY,
         "triggered_by_event_id": None,
+        "started_event_id": ANY,
         "emission_sequence": ANY,
         "value": "saving value",
         "metadata": {"task": "test_task"},
@@ -411,6 +414,7 @@ def test_external_memory_save_events(
         "parent_event_id": ANY,
         "previous_event_id": ANY,
         "triggered_by_event_id": None,
+        "started_event_id": ANY,
         "emission_sequence": ANY,
         "value": "saving value",
         "metadata": {"task": "test_task"},