Refactor namespaces to follow new naming convention and add item model classes

Models/Enums/ItemEnums.cs

@@ -0,0 +1,25 @@
+namespace Pet.Companion.Models.Enums
+{
+    public enum ItemType
+    {
+        Consumable,
+        Equipment,
+        Material
+    }
+
+    public enum ItemRarity
+    {
+        Common,
+        Uncommon,
+        Rare,
+        Legendary
+    }
+
+    public enum EquipmentSlot
+    {
+        Helmet,
+        Chest,
+        Leggings,
+        Weapon
+    }
+}