fix: message_type inconsistency across message end points (#10108)

The `before_type_cast` method sometimes returns a string for
`message_type`, creating inconsistencies in different payloads. This
pull request will remove all `before_type_cast` usage and replace it
with `to_i` methods.

app/views/api/v1/models/_conversation.json.jbuilder

@@ -17,7 +17,7 @@ json.messages do
     json.content message.content
     json.id message.id
     json.sender_name message.sender.name if message.sender
-    json.message_type message.message_type_before_type_cast
+    json.message_type message.message_type.to_i
     json.created_at message.created_at.to_i
   end
 end