Changes to Bulk-upsert one item's price rows from the item price sheet (bulk admin entry / re-import of the exported `.xlsx`). Body fields match M:IO.CommonAPI.Controllers.v1.Catalog.ItemPricesController.DownloadXlsx(System.Int32,IO.Domain.Shared.Enums.PriceType,IO.Catalog.Contracts.DTO.Pricelists.ItemPricesExportRequest,System.Threading.CancellationToken)'s columns exactly; an empty `companyCode` targets the item's base price. Returns the count upserted.