Non-centered Bounding boxes not respected

[Telzhaak]

Hello,

1. noice crate, thank you for the work!
2. non-centered boxes are not handled correctly internally

The Voronoi-algorithm for example uses BoundingBox::is_inside()

is_inside = point.x.abs() <= self.top_right.x && point.y.abs() <= self.top_right.y

which only works for centered boxes.

Similarily which_edge()

if point.y == self.top_right.y {
    // top
    BoundingBoxTopBottomEdge::Top
} else if point.y == -self.top_right.y {
    BoundingBoxTopBottomEdge::Bottom
} else {
    BoundingBoxTopBottomEdge::None
}

relies on mirrored coordinates around the origin (0,0)

point.y == -self.top_right.y

---

The simplest solution would be to add a private centered_bounding_box-variable to the VoronoiBuilder.

1. Center arbitrary bounding_box by subtracting BoundingBox.center() from every site
2. Use this centered centered_bounding_box in all calculations (which is the current working state)
3. Reapply shift back to every obtained vertex/centerpoint

However, this is problematic, if users can access the algorithm directly, without using VoronoiBuilder, because they could supply noncentered boxes instead which results in something like this: 25 different Voronoi-Diagrams with different Bounding boxes. The blue cross is the world origin, and the red dots in the 3 quadrants (right-up, right-down, left-down) are sites for which no Voronoi-Diagram could be generated