Add a registration mechanism to Aggregators#30

Draft

devavret wants to merge 2 commits intorapidsai:velox-cudffrom

devavret:register-aggs

Commits on Jun 9, 2025

Add aggregator registration mechanism and function to register ones with presto prefix
devavret
committed

Commits on Jun 10, 2025

register companion aggs separately instead of wrangling with their names
devavret
committed