New pixel splitting implementation

[kif]

• should be able to deal with polygonal pixel with any size, (obviously 3, 4 and 6, but one could imagine edge splitting for better representativeness. The amount of work scales with the number of edges O(n), thus better than oversampling which is in O(n²)
• Probably implemented in Cython, but it would be a good use case for Rust + PyO3
• Define a Polygon class which constructor has just the number of edges (or vertices). One can reasonably assume a convex polygon, it simplifies some maths.
• Use setters to define vertices position
• Has a bounding-box, subtract the minimum integer position ...
• Has a isinside method to assess if a position is completely inside the polygon.

[kif]

The bug #2631 is related to the implementation of pixel-splitting where quasi vertical edges combined with numerical noise (consequence of float32 for maths) introduced out-of-bound memory access (hence the seg-fault)

This bug #2631 should just be addressed by ensuring no "out-of-bound" access is performed. The issue with the math and the numerical precision should be addressed here.