Batched Events must not get lost

[Structed]

In case of a crash/scene change etc, unsent events should be persisted to disk and sent the next time the game can send it.

Disc access rate is a concern:

1. less disk access - higher chance of loss of events
2. higher disk access - lower chance of loss of events

Idea/Request by @lentsius-bark

• [ ] Write batch to file system (single file) every time an event is added to a batch
• [ ] Delete/overwrite batch after send
• [ ] On game start, read cache and send batch
• [ ] Add documentation