sgp40: Add sgp40 support

[meteyou]

Add support for the SGP40 Sensor for VOC mesurement. This sensor needs a temp + huminity sensor to work correct. If you don't add one, it will use 25°C and 50% huminity as reference.

Here is an example config:

[temperature_sensor BME_OUT]
sensor_type: BME280
i2c_address: 118
i2c_mcu: pico
i2c_bus: i2c1e
i2c_speed: 400000

[temperature_sensor SGP_OUT]
sensor_type: SGP40
i2c_mcu: pico
i2c_bus: i2c1e
ref_temp_sensor: bme280 BME_OUT
ref_humidity_sensor: bme280 BME_OUT

Link to discourse: https://klipper.discourse.group/t/support-for-sgp40-sensors/20033

[github-actions]

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[thetic]

this library requires at least python 3.6¹, but klipper is still testing against python 2. I'm sure this is intentional, but I'm not sure why. It went end of life years ago².

Footnotes

1. https://pypi.org/project/sensirion-gas-index-algorithm/ ↩

2. https://www.python.org/doc/sunset-python-2/ ↩