message: fix message timestamp typing
diff: @@ -165,7 +165,7 @@ export interface Message {
  /** The contents of the message */
  content: string;
  /** When this message was sent */
  - timestamp: string;
  + timestamp: number;
  /** When this message was edited (if it was not edited, null) */
  editedTimestamp?: number;
  /** Whether this was a TextToSpeech message. */
  