Ambient light sensors can be quite sensitive and the LightLevel
property might be changing very often. That has two undesired
consequences:
* The `als_enabled_state_changed` callback gets constantly called
due to a change in a property which it does not care about, as
only `HasAmbientLight` is relevant. Therefore, limit the code
execution to when something needs to be changed.
* During debugging, the terminal gets spammed with "ALS enabled: on/off"
messages.
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