Limit Invalidation to Current Radius Bounded Connected Region

[william-silversmith]

Sometimes when a neuron twists, the invalidation pass can eliminate useful branches that are connected from a more distant point. It would be possible, and possibly practical to:

1. Label all elements within the invalidation zone.
2. Run connected components
3. Mask out all components that the current path lies outside
4. Proceed with invalidation normally (ignoring those masked components)

This would be slower, so maybe hide it behind a flag?

[william-silversmith]

Thanks for Forrest's mesh TEASAR for the inspiration (it has this feature already via a different method).

[william-silversmith]

A good example of the kind of issue this would prevent (here we used scale=10x, const=200)