mp.Volume(vertices=...) is not a bounding box (& is undocumented)

[yurivict]

In the modified example bent-waveguide.ipynb the 'vertices' argument has 6 elements:
bent-waveguide-1.ipynb

The span of the vertices array is -1.5 .. +1.5 in both X and Y directions.
However, the displayed box is has the width < 1:

mp.Volume should either throw an exception if the vertices argument isn't valid, or it should display it properly.
The above shape doesn't make sense.

[stevengj]

@smartalecH added this vertices option to the mp.Volume construct in #910.

Right now, it uses the centroid (mean) of the vertices to determine the volume center, but to determine the volume size it only uses the first two elements of the vertex list?

It seems like it would be better to use define the volume as a bounding box for the vertices? In any case we should document precisely what this does. And we should emphasize that the final mp.Volume is a Cartesian box, not a polygon (see the confusion in #2905).

@smartalecH, I'm not 100% sure what the intended use of this feature is?