CacheManager: does not wait for data to be persisted. Potential consistency issue

## 🐛 Bug Report

due to data consistency issues with JsonCacheInfoRepository, reported in https://github.com/Baseflow/flutter_cache_manager/issues/491, i started checking if i could use 'CacheObjectProvider', it looks fine, but the same issue can occur because cachemanager doesn't wait for data to be persisted because it is missing an "await" on line 232. is this intentional? why?

### Expected behavior

### Reproduction steps

### Configuration

**Version:** 1.x

**Platform:**
- [x] :iphone: iOS
- [x] :robot: Android

Inspect CacheManager around line 232 and trace how it persists data through JsonCacheInfoRepository or CacheObjectProvider. First run the existing package tests and look for coverage of persistence ordering; done means the manager does not return before the relevant data is persisted and consistency behavior is covered by a regression test.

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