Shard the SpaceManager

(Missing Feature, Closed -> Fixed, Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Scalability
Summary: I suspect that the SpaceManager needs to be split, with the routing becoming just Cluster Sharding and other functions becoming a separate Actor or Ecot. (Is there anything here that can't be run in a UserSession or UserSpaceSession?)