refactor(Statemachine): 引入CooldownTimer类重构攻击冷却逻辑

将攻击冷却逻辑从EntityBase中提取到独立的CooldownTimer类
简化EntityBase代码并提高可维护性

scripts/Statemachine/CooldownTimer.gd

@@ -0,0 +1,12 @@
+class_name CooldownTimer
+
+var cooldown: float = 100
+var lastStart: int = 0
+
+func isCooldowned():
+	return WorldManager.getTime() - lastStart >= cooldown
+func startCooldown():
+	var state = isCooldowned()
+	if state:
+		lastStart = WorldManager.getTime()
+	return state