Function spawn_token_refresh_task 

pub fn spawn_token_refresh_task(
    expires_in: u64,
    refresh_token: String,
    cmd_tx: UnboundedSender<HandlerCommand>,
    cancel_token: CancellationToken,
)

Spawns a background task to refresh the authentication token before it expires.

The task sleeps until 80% of the token lifetime has passed, then sends a refresh request. When the refresh succeeds, a new Authenticated message will be received, which triggers another refresh task - creating a continuous refresh cycle.

The cancel_token allows the caller to cancel a stale refresh task when a new authentication cycle begins (e.g., after reconnection re-auth).