Message status
Notification of the status of an outbound message (`type: status`).
A single message can generate several events in order: `sent`, `delivered`, `read`. The `failed` status is terminal (no more events are received after it). Other possible statuses are `no_active_session` (the message fell outside an active session) and `reply`.
Not all messages reach `read`; it depends on whether the user has read receipts enabled. The order may vary: in some cases `delivered` and `read` are received almost simultaneously.

