def last_downtime
      send_message!(Protocol::Device::GetInfo.new,
         wait_for: Protocol::Device::StateInfo) do |payload|
        payload.downtime.to_f / NSEC_IN_SEC
      end
    end
def last_downtime
      send_message!(Protocol::Device::GetInfo.new,
         wait_for: Protocol::Device::StateInfo) do |payload|
        payload.downtime.to_f / NSEC_IN_SEC
      end
    end
Return device last downtime
 @api private
 @return [Float] Device's last downtime in secodns