DTOs for index mostly done, doing DB models

SVSim.EmulatedEntrypoint/Models/Dtos/UserItem.cs

@@ -0,0 +1,13 @@
+using MessagePack;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos;
+
+[MessagePackObject]
+public class UserItem
+{
+    [Key("item_id")]
+    public int ItemId { get; set; }
+    
+    [Key("number")]
+    public int Number { get; set; }
+}