Add initial project files and configurations for Unity setup

Assets/Scripts/Core/Ports/IPersistenceService.cs

@@ -0,0 +1,8 @@
+namespace Core.Ports
+{
+    public interface IPersistenceService
+    {
+        void Save(string key, int value);
+        int Load(string key, int defaultValue = 0);
+    }
+}