I used magnetic proximity sensors which are widely used in industry for this type of function; the sensor is https://www.digikey.com/products/en?keywords=59145-010 and the matching magnet is https://www.digikey.com/products/en/sensors-transducers/magnets-sensor-matched/566?k=57145-000.
You’ll need to work out how to mount them, here’s a picture of one of mine:
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