getKeysets method
get all keysets if no mintUrl is provided \
Implementation
@override
Future<List<CahsuKeyset>> getKeysets({String? mintUrl}) {
if (cashuKeysets.containsKey(mintUrl)) {
return Future.value(cashuKeysets[mintUrl]?.toList() ?? []);
} else {
return Future.value(cashuKeysets.values.expand((e) => e).toList());
}
}