Speed up action of a matrix on a polygon

[saraedum]

In this trivial example, the runtime goes from 122µs to 66μs.

sage: from flatsurf import polygons
sage: p = polygons(vertices = [(1,0),(0,1),(-1,-1)])
sage: r = matrix(ZZ,[[0,1], [1,0]])
sage: %timeit r*p