make Attribute a struct again

Assets/Scripts/Attribute.cs

@@ -1,10 +1,14 @@
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
-public class Attribute : ScriptableObject
+[Serializable]
+public struct Attribute
 {
-    public long Base { get; set; }
+    public long Base;
+
+    public Attribute(long stat) { Base = stat; }
 
     /// <summary>
     /// Calculates the stat value with accumulated buff and debuff modifiers.