iOS 12 support and fix bugs

[NguyenASang]

Fix lag when changing brightness and brightness changes after respring

First, I don't have any devices with iOS 13+, so I need someone to test it on other iOS.

Before (actually not as much as the video, just slightly):

https://github.com/jschiefner/advanced-brightness-slider-tweak/assets/87893636/9dbbce82-590c-4dd6-a244-bb5587b223df

After:

https://github.com/jschiefner/advanced-brightness-slider-tweak/assets/87893636/ce8b87fe-d029-45d2-ac5b-5b6e89c2451f