feat: avoid schema version bump for temporary spaces

Temporary spaces, used for cluster-wide SQL data materialization,
were causing unnecessary netbox schema version bumps, leading to
schema downloading via netbox, excessive Lua garbage and GC blocks.
Since these tables are for internal SQL use, we don't need to inform
netbox clients about schema changes. We now maintain separate schema
versions: one for netbox clients and one for the internal prepared
statement cache.

NO_DOC=picodata internal patch
NO_CHANGELOG=picodata internal patch