[FIX] Switch Characteristics code to promise-based functions

[johannrichard]

Describe the enhancement
Consider using the promise-based Characteristic.onGet and Characteristic.onSet method instead of the current Characteristic.onmethods.

Examples and context

homebridge-dingz/src/dingzAccessory.ts

Lines 339 to 342 in f724931

	// create handlers for required characteristics
	temperatureService
	.getCharacteristic(this.platform.Characteristic.CurrentTemperature)
	.on(CharacteristicEventTypes.GET, this.getTemperature.bind(this));

Additional context
See Homebridge Characteristics documentation.