sendTyping method
只支持单聊
Implementation
Future<void> sendTyping({
  required String userId,
}) {
  return checkResult(ChatSDKEvent.sendTypingMessage, () async {
    Message msg = Message.createCmdSendMessage(
      targetId: userId,
      action: typingKey,
      deliverOnlineOnly: true,
    );
    await Client.getInstance.chatManager.sendMessage(msg);
  });
}