логика сборки + логика покупок (подкорректированы purchaseBinding и BuildSearch)

ComputerHardwareStore/ComputerHardwareStoreDataModels/Models/IPurchaseModel.cs

@@ -2,10 +2,9 @@
 {
     public interface IPurchaseModel : IId
     {
+        int VendorId { get; }
         double Cost { get; }
         DateTime DateCreate { get; }
-        int VendorId { get; }
-        double Sum { get; }
         public Dictionary<int, (IBuildModel, int)> PurchaseBuild { get; }
         public Dictionary<int, (IProductModel, int)> PurchaseProduct { get; }
     }