MessageBuilder improperly folds long email addresses inside the address token

[nogringo]

When generating a MIME message with a very long email address (e.g., a Nostr npub address), the MessageBuilder incorrectly inserts a folding sequence (\r\n\t) inside the email address itself.

void main() {
  final builder = MessageBuilder()
    ..from = [MailAddress(null, 'npub1mlfgj95gv89tdjemt2jc4jqvn4dumhujeymzv20ljqywcfupwz5s09pe55@testnmail.uid.ovh')];
  final mimeMessage = builder.buildMimeMessage();
  final rendered = mimeMessage.renderMessage();
  print(rendered);
}

The renderer should avoid folding inside an addr-spec token.