Enable strict type checking on apple_tv integration (#101688)
* Enable strict type checking on apple_tv integration
* move some instance variables to class variables
* fix type of attr_value
* fix tests for description_placeholders assertion
* nits
* Apply suggestions from code review
* Update remote.py
* Apply suggestions from code review
* Update __init__.py
* Update __init__.py
* Update __init__.py
* Update config_flow.py
* Improve test coverage
* Update test_config_flow.py
* Update __init__.py
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Co-authored-by: Joost Lekkerkerker <joostlek@outlook.com>
Co-authored-by: Erik Montnemery <erik@montnemery.com>
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