effect method
Adds an Effect which has no visual effect. Occasionally useful for
setting inheritable delay, duration, and curve values.
Implementation
T effect({
  Duration? delay,
  Duration? duration,
  Curve? curve,
  double? begin,
  double? end,
}) =>
    addEffect(Effect(
      delay: delay,
      duration: duration,
      curve: curve,
      begin: begin,
      end: end,
    ));