clampSpeed method
Clamps velocity to maxSpeed if set, preserving direction.
Implementation
Offset clampSpeed(Offset velocity) {
final cap = maxSpeed;
if (cap == null) return velocity;
final speed = velocity.distance;
if (speed <= cap || speed == 0) return velocity;
final scale = cap / speed;
return Offset(velocity.dx * scale, velocity.dy * scale);
}