AirPurifier Miot: `aqi` field is PM2.5 density instead of AQI.

[MPThLee]

Describe the bug Somehow, The AQI field on status is represent pm2.5 density. not aqi. AQI is should be average_aqi only.

But some older model like 3 series are only present pm2.5 density without AQI calculation. so may need break changes.

See the miot-specs for there varients.