serialize method
Implementation
@override
String serialize(
  int type,
  Uint8List sealed,
  Uint8List iv, {
  Uint8List? senderPublicKey,
}) {
  List<int> l = [type];
  if (type == EncodeOptions.TYPE_2) {
    l.addAll(sealed);
    return base64Url.encode(l);
  }
  if (type == EncodeOptions.TYPE_1) {
    if (senderPublicKey == null) {
      throw const ReownCoreError(
        code: -1,
        message: 'Missing sender public key for type 1 envelope',
      );
    }
    l.addAll(senderPublicKey);
  }
  // l.addAll(iv);
  l.addAll(sealed);
  return base64Encode(l);
}