feat(保存系统): 改进保存数据的序列化和反序列化处理

重构保存系统以使用新的嵌套字典工具方法
修改Starter场景中的按钮文本并隐藏多人游戏选项
添加JsonTool和ArrayTool的嵌套数据操作方法

scripts/Tools/ArrayTool.gd

@@ -53,3 +53,34 @@ static func mergeDictionary(a: Dictionary, b: Dictionary) -> Dictionary:
 	for key in b:
 		result[key] = result.get(key, 0.0) + b[key]
 	return result
+static func getNested(data: Variant, path: String) -> Variant:
+	var keys = path.split(".")
+	var result = data
+	for key in keys:
+		if result is Dictionary:
+			result = result[key]
+		elif result is Array:
+			result = result[key.to_int()]
+		else:
+			return null
+	return result
+static func setNested(data: Variant, path: String, value: Variant):
+	var keys = path.split(".")
+	for i in range(keys.size() - 1):
+		var key = keys[i]
+		if data is Dictionary:
+			data = data[key]
+		elif data is Array:
+			data = data[key.to_int()]
+		else:
+			return
+	var lastKey = keys[-1]
+	if data is Dictionary:
+		data[lastKey] = value
+	elif data is Array:
+		var index = lastKey.to_int()
+		if index == data.size():
+			data.append(value)
+		else:
+			data[index] = value
+	return data