Memory Size Estimation on UpsertTable

We need tooling to estimate the memory/disk size for the upsert table based on primary keys and their cardinalities.

Start by finding the UpsertTable implementation and any existing memory or disk size estimation tooling. Define how primary-key cardinalities feed the estimates and how representative upsert-table data will validate them. Done means the tooling reports both memory and disk size for an upsert table.

Written by the indexing model from the issue text.