add Message status attribute for V2+ Message Model

[leeyisoft]

Regarding the issue of the Message status attribute, although there is a method and perfection to calculate the status through the relevant time, I think a status data should still be added to the Message model:

Trading space (storing one more field) for time (performance) + reliability (data consistency) + maintainability is worth it!

The existing method is a computational load and I cannot set the status:

  /// Calculates the current status of the message based on its timestamps.
  /// Returns `null` if the message has no specific status yet (only `createdAt`).
  MessageStatus? get status {
    // Message status is determined by the most recent state change in the message lifecycle.
    // The order of checks matters - we check from most recent to oldest state.
    // Note: createdAt, updatedAt, and deletedAt are message states rather than statuses.
    if (metadata?['sending'] == true) return MessageStatus.sending;
    if (failedAt != null) return MessageStatus.error;
    if (seenAt != null) return MessageStatus.seen;
    if (deliveredAt != null) return MessageStatus.delivered;
    if (sentAt != null) return MessageStatus.sent;
    return null;
  }

[demchenkoalex]

will be added (converted to issue)