Performance issues as number of vertices increases for intersection operations

[olly-writes-code]

Hi @AngusJohnson! Thanks for the wonderful library.

I've been hacking away on some python bindings at pyclipper2.

All the time I'm comparing vs shapely which is my go-to for geometric operations. I came across Clipper while reading the FreeCAD forums so I wanted to give it a go.

I did some benchmarking. For small geometries I see that Clipper2 is roughly 5x faster than shapely but as the number of vertices for the intersecting geomtries (or paths) increases the performance drops off. Here's a chart with some increasing complicated shapes (50 -> 1000 vertices) interesecting a circle.

It seems strange to me that performance degrades so substantially around the 250 vertices mark. Any initial thoughts? Anything I can do to help uncover what might be going on here?

Thanks again!