* Initial changes to resolve issue 16733
Added logic to ensure that if the state is unknown during startup that the error about being unable to parse the value is not logged.
Further, also ensured that if an attribute is set to None it does not try to convert the None value to Fahrenheit as that will cause an error.
* Cleaned up and added few comments
Cleaned up some lines based on flake8 and pylint.
Added some comment lines on the items added.
* Changed to async and using async_added_to_hass
Changed sensor to use async.
Registering state tracking for sensors and initial setup is now done upon the home assistant start event.
* Updated test and small fix
Updated test to handle unavailable state of sensor and return of None for attributes when data is unavailable.
Ensured that atributes are set to None when state is unavailable due to incorrect data.
* Fixed some flake8 issues in test
Fixed some flake8 issues in test_moldindicator.py.
* Updates based on review
Updates based on review from MartinHjelmare
* Added sensor entity_id to logger errors
Added sensor entity_id to logger error messages
Update test to use constant STATE_UNKNOWN instead of fixed string.
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