- Removed obsolete `new` keywords.
 - Added types to collection and function variables.
 - Added `final` and `const` keywords.
 - Replaced `null` guards with concise `?.` and `??` operators.
 - Added missing null check on `dispose` for `FadeAnimatedTextKit`.
 - In `fade.dart`, renamed the `_RotatingTextState` class to `_FadeTextState` to be consistent with the overall pattern and avoid confusion with `_RotatingTextState` in `rotate.dart`.

**Warning**:
 - Removed `onNextBeforePause` from `ColorizeAnimatedTextKit` because it was not referenced.

…ul Widget name better.

… to some AnimatedBuilders, and added const keyword.