Bulk Fulfillment: Another Speed Pass

Fulfilling many orders at once is faster. The job that runs each order's allocation and fulfillment used to repeat the same database work for every order it processed; that cost added up during large bulk fulfillments and kept database locks held longer than necessary. That redundant work is gone across inventory allocation, fulfillment materialization, and the fulfill command's order validation. Nothing changes about what fulfillment does — just how much it does per order.