fix: revert class attributes removal

Signed-off-by: Yves Bastide <yves@botify.com>

Author: ybastide

simpleflow/swf/mapper/models/event/base.py

@@ -42,10 +42,11 @@ class Event:
     :param  raw_data: raw_event representation provided by amazon service
     """
 
-    _type: str | None
-    _name: str | None
-    _attributes_key: str | None
-    _attributes = Any
+    # These class attributes manipulate instance ones
+    _type: str | None = None
+    _name: str | None = None
+    _attributes_key: str | None = None
+    _attributes = None
 
     excluded_attributes = ("eventId", "eventType", "eventTimestamp")