TypingIndicator constructor
      
      TypingIndicator({})
     
    
Constructs a new TypingIndicator instance.
Requires sender, receiverId, receiverType, and lastTimestamp to be specified. metadata is optional.
Implementation
TypingIndicator({
  required this.sender,
  required this.receiverId,
  required this.receiverType,
  this.metadata,
  required this.lastTimestamp,
});