* Update AIAgent,Run to take IEnumerable instead of IReadonlyCollection
* Address PR comment.
* Cast to IReadonlyCollection since this is typically all that is required to avoid unecessary allocation.
* Update OrchestratingAgent protected methods as well.
The previous fix for the aggregation in AIAgentHostExecutor has a bug wherein we only include the first update from a ChatMessage in the outgoing "collected" message.
The fix is to ensure we put the collected updates into the message before sending it out.