CacheManager saves files with the same path

## 🐛 Bug Report

Scheduled file cleanup on CachedNetworkImage throws `FileSystemException: Cannot delete file`. [Issue](https://github.com/Baseflow/flutter_cached_network_image/issues/335)
After research, it turned out that different images are recorded along the same path. This happens because relativePath encoding uses Uuid().v1() , which uses DateTime.now() , which causes our error when loading a lot of files at the same time.

To solve this problem, changing the path encoding in _flutter_cache_manager-3.3.0/lib/src/cache_manager.dart_ `putFile` and `putFileStream` should help. for example, change **v1** to **v4**, which uses a more random encoding

```
> cacheObject ??= CacheObject(
> url,
> key: key,
> relativePath: '${const Uuid().v1()}.$fileExtension',
> validTill: DateTime.now().add(maxAge),
> );
```

Read flutter_cache_manager-3.3.0/lib/src/cache_manager.dart, focusing on putFile and putFileStream and how relativePath is encoded. Confirm that concurrent image writes no longer receive the same path, and that scheduled cleanup can delete the resulting files without a FileSystemException.

由索引模型根据 Issue 内容生成。