Maintaining sorted neighbor lists by most likely surface

[gridley]

Description

In ANS M&C 2025, I overheard that Serpent sorts neighbor lists by the surface crossing frequency in order to first check for intersections with the most likely surface. It is apparently taken care of in a preprocessing step. Since the current lists are maintained on-the-fly, this would be an interesting upgrade to attempt.

Compatibility

This is a purely back-end optimization.