Hack the ZoneTableSegment into MemoryClient
This branch needs the MemoryClient to have its Zonetablesegment. But it doesn't have one now and it is not the task of this branch to put it in there. So I added it inside in somewhat ad-hoc manner. This is hairy and adds bunch of temporary methods. If there's a better approach, let's use it. But taking this for now to be cleaned up in some follow-up ticket.