fix: persist on_event_callback mutations before session append#5021

Jholly2008 wants to merge 2 commits intogoogle:maingoogle/adk-python:mainfrom

Jholly2008:kkk/fix-on-event-callback-persistenceJholly2008/adk-python:kkk/fix-on-event-callback-persistenceCopy head branch name to clipboard