subscription method
Implementation
Future<NostrRequest> subscription(Filter filter, RelaySet relaySet,
{bool splitRequestsByPubKeyMappings = true}) async {
return doNostrRequest(
NostrRequest.subscription(Helpers.getRandomString(10), eventVerifier: eventVerifier), filter, relaySet, splitRequestsByPubKeyMappings: splitRequestsByPubKeyMappings);
}