ROIs could use reworking

[barrettMCW]

currently use skimage for turning omero ROIs into contours. It's pretty slow. We also have a broken mask function that was removed.

Actionables:

• performant conversion from a given shape and minimal points (rectange, ellipse, polygon, etc) into contours.
• performant conversion from a given contour (or shape definition?) into a mask.

drawing a given shape should be in a good spot thanks to pyvips svg drawing as seen in lavlab.imsuite.draw_shapes()