getBlob abstract method
Gets a blob by trying servers sequentially until success
If authorization is null, the server must be public
If start and end are null, the entire blob is returned
start and end are used to download a range of bytes, @see MDN HTTP range requests
Implementation
Future<BlobResponse> getBlob({
required String sha256,
required List<String> serverUrls,
Nip01Event? authorization,
int? start,
int? end,
});