[meraki] switch.port.status.usage.* and throughput.* always report 0

The device_health metricset passes the collection period (capped at 300s) as the timespan for GetDeviceSwitchPortsStatuses, but Meraki collects port usage data periodically and documents the last ~5 minutes as potentially incomplete, so switch.port.status.usage.* and throughput.* are always 0.