Cache hit/miss metrics

## 🏗 Enhancement Proposal

Have cache manager keep a count of cache hit/misses during use.

### Pitch

Something that popped into my head while testing for #179, it would be useful for the cache manager to store cache hit/miss counts. This would allow app developers to better understand how the cache is performing, and adjust usage to improve cache hit rates.

### Platforms affected (mark all that apply)
- [x] :iphone: iOS
- [x] :robot: Android

首先在 repository 中追踪 cache manager 的缓存查找和存储路径，因为 issue 没有指定文件或测试。确定 hit 和 miss 事件发生的位置，以及应如何为 iOS 和 Android 的使用公开计数；完成的标准是，在使用过程中维护 cache hit/miss 计数，并由相关测试覆盖。

由索引模型根据 Issue 内容生成。