scaling method
Wraps this particle with a ScalingParticle.
Allows for changing the size of this particle and/or its children.
Implementation
ScalingParticle scaling({double to = 0, Curve curve = Curves.linear}) {
  return ScalingParticle(
    to: to,
    child: this,
    lifespan: _lifespan,
    curve: curve,
  );
}