Implementation flaw

Hi there,

I think there is an implementation error in the sample project - more specifically, a flaw in the design of CKSyncEngine.
In the SyncedDatabase file, line 350:

self.syncEngine.state.add(pendingRecordZoneChanges: pendingSaves)

This tells the syncEngine what to do when the time is right. Since this piece of information is *not* persisted in this call (I think its persisted in .stateUpdate(let event)), there is a chance that this information is lost if the app crashes between .add(pendingRecordZoneChanges: pendingSaves) and .stateUpdate(let event).

I know this is just a sample project, but I really think this is a flaw in the API design of CKSyncEngine since I do not see an easy way to guarantee correct behavior. A simple fix would be to make .add(pendingRecordZoneChanges: pendingSaves) (and similar methods) async and only complete after .stateUpdate(let event) was called.

What do you think?

从 SyncedDatabase 的第 350 行开始，检查 pendingRecordZoneChanges 和 stateUpdate 事件的处理方式。评估 issue 中描述的崩溃窗口以及提议的异步 API 更改；只有在 maintainer 确认已解决数据丢失或 API 设计方面的问题后，才算完成。

由索引模型根据 Issue 内容生成。