New Device: Proscenic A8 air purifier

[ak6i]

Describe your device
Air purifier with 3 speeds and auto mode, and built-in air quality sensor.

Partial Support?
Works partly - unable to control speed; several errors appear in logs on status updates; Homekit gets stuck showing "Turning off..." presumably due to the aforementioned errors. I've also seen it get stuck in "Turning on..." mode.

Device Schema
Close to the schema declared in AirPurifierAccessory.js, but:

• no DP_MODE value (id 3 is absent) - this may be a cause of the "Turning off..." issue
• DP_FAN_SPEED values are different (id 4 = 'sleep', 'mid', 'high' or 'auto') - this is why the speed can't be controlled, and the fact that these values are not numeric may also be a cause of the "Turning off..." issue
• DP_AIR_QUALITY is on id 21, and like the Breville, returns 'great' - this is not an issue since air quality is derived from the PM2.5 reading
• field 101: appears to be the number of hours the timer is set for. There's a button on the top that sets the timer for 2, 4 or 6 hours, and field 101 shows 2, 4 or 6 in these cases. When the timer is not set, field 101 is 0.
• field 102: has always been 003 in my testing.

Example:
{
'1': true,
'2': 0,
'4': 'sleep',
'5': 97,
'7': false,
'8': false,
'11': false,
'16': 1959,
'17': 0,
'21': 'great',
'101': 0,
'102': '003'
}

Additional context
Supporting this in a nice way will require not only special handling for the fan speed labels, but also mapping the auto mode to and from DP_FAN_SPEED.

This is the finding from my preliminary research into the issue. I haven't yet read about how to test Homebridge plugins but I'm prepared to give it a go. Javascript isn't my main language but the code seems easy enough to follow so I'm hoping I can give it a go and provide a PR for this issue.