Inventory Reservations

A store's starting inventory is given as stock, a dict mapping SKU to available quantity. Orders arrive as reservations, a list of [order_id, items], where items is a list of [sku, qty] lines.

Process reservations in list order. Each reservation is all-or-nothing:

• First combine lines for the same SKU within the order (two lines of ["milk", 1] need 2 milk).
• The reservation is accepted only if, for every SKU it needs, the remaining quantity is at least the combined amount. A SKU missing from stock has quantity 0.
• An accepted reservation subtracts its quantities from the remaining stock. A rejected one changes nothing.

Return [accepted, final_stock], where accepted is a list of booleans (one per reservation, in order) and final_stock is a list of [sku, remaining_qty] rows for every SKU in the starting stock, sorted by SKU ascending.