FluxAnimationInit<T> typedef
FluxAnimationInit<T> =
FluxAnimation<T> Function(T value, T velocity)
A function that creates a FluxAnimation from an initial value and velocity.
Used by ManualAnimation to create the "coast" animation when the user lifts their finger — the spring picks up from the gesture's velocity.
Implementation
typedef FluxAnimationInit<T> = FluxAnimation<T> Function(T value, T velocity);