[TESTING] Write unit tests for temperature and CO2 sensors

[ezehf2]

Create tests/test_temperature_sensor.py and tests/test_co2_sensor.py. Each file must test four things — that generate_reading() returns valid JSON, that all required fields are present (sensor_type, room, value, unit, timestamp), that the value falls within the expected range (temperature 18–30°C, CO2 400–1500 ppm). That drift between consecutive readings does not exceed a reasonable step (temperature max 1 degree per reading, CO2 max 50 ppm per reading). Run with pytest tests/ and paste the passing output as a comment on this issue before closing.

[mbaj2]