getAnimatedOpacity method
Optional: Override to provide dynamic opacity for particles.
Returns opacity multiplier 0.0 - 1.0 for effects like depth-based fading.
Default returns null (use particle's original color opacity).
particle - The particle to get opacity for
animationProgress - Elapsed time in seconds, scaled by animationSpeed
Implementation
double? getAnimatedOpacity(Particle particle, double animationProgress) =>
null;