FirebaseCacheManager uses DownloadUrl which has a token in the url defeating cache

[FirebaseCacheManager](https://github.com/Baseflow/flutter_cache_manager/blob/develop/flutter_cache_manager_firebase/lib/src/firebase_http_file_service.dart#L36) uses the `ref.getDownloadUrl()` which typically returns a url with a dynamic access token in the query string of the URL. Doesn't that mostly defeat the purpose of the cache, assuming that the key of the file in the cache is tho whole url including the token?

Start in flutter_cache_manager_firebase/lib/src/firebase_http_file_service.dart at the referenced line, then trace how the download URL becomes the cache key. Check whether changing Firebase access tokens creates separate cached entries; done means the cache behavior is verified and the reported concern is resolved with coverage for the relevant case.

索引モデルが issue の本文から書いたものです。