resolveVelocity method
Implementation
@override
Offset resolveVelocity(int index, int total, Random rng) {
final angle = (index / total) * 2 * pi + rng.nextDouble() * 0.1;
final speed = minSpeed + rng.nextDouble() * (maxSpeed - minSpeed);
return Offset(cos(angle) * speed, sin(angle) * speed);
}