move msgs into AppType.app_type, and refactor AppUpdate.update function to have type (app_type -> app_type) instead of pervious case which was (app_type -> app_type * MailboxType.t list). Reason: no need to allocate/return tuple when can store messages in type directly; previous msg list will be reset after each app update. All tests after refactor are passing.

fcore/build-search-list.sml

@@ -73,6 +73,7 @@ struct
             val buffer = LineGap.goToIdx (origIdx, buffer)
             val searchList = SearchList.goToNum (origIdx, searchList)
           in
+            (* todo: probably change return type to (buffer * searchList) later *)
             AppWith.searchList (app, searchList, buffer, searchString)
           end
     end