Create Order Batch

Place up to 10 orders in one request.

All orders must share one subaccount_id. Items are validated independently: an invalid item is rejected in its per-index result while valid items proceed, so the response is 202 Accepted even when some (or all) items fail validation. Generic asset orders are not supported in batches. Accepted orders are queued for execution exactly like POST /v1/orders; track fills and rejections via GET /v1/orders/{order_id} or the orders websocket.