Numpy acceleration of stitches without requirement.

[tatarize]

There are a few places where numpy arrays should be usable but because of early code it currently is not permitted to simply pass a 2d Nx2 array to become a block. Rather than checking if a passed item is a tuple or a list it should simply duck cast for whether it's an iterable with 2-3 items wide. This would also allow the addition of generators and other classes not previously covered.

Fixing this should also go back to EmbroiderPy/vpype-embroidery and update the relevant reading and writing code elements.