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),
> );
```

Leggi flutter_cache_manager-3.3.0/lib/src/cache_manager.dart, concentrandoti su putFile e putFileStream e sul modo in cui viene codificato relativePath. Conferma che le scritture concorrenti di immagini non ricevano più lo stesso percorso e che la pulizia pianificata possa eliminare i file risultanti senza una FileSystemException.

Scritto dal modello di indicizzazione a partire dal testo della issue.