Improve accuracy of Helper.cubicRoots()

Use final newton root refinement in cubic roots solve to refine accuracy
For clip intersections (xPoints, yPoints), ensure x(t) or y(t) are outside of the clip (side issue) => extra clip padding will then be useless (1.0 for float, 0.25 for double variants) as roots do not ensure enough precision on the point coordinates for now

Provide feedback