[FEA] Support unspilling or caching of materialized spilled buffers

[zpuller]

Is your feature request related to a problem? Please describe.
Followup from #11880 (comment) - if we spill to disk once, then at that point each time we want to read that data again, even if a copy is sitting in host memory, we have to read it from disk again and add another copy of it to host memory.

Describe the solution you'd like
We still need to figure out exactly what we want to support