Add safety calculator for visualization

[sethrj]

DRAFT because this is an unpolished work in progress: it should be cleaned up and added to celer-geo .

This adds a helper function that lets us evaluate the safety distance on a grid of points (for now, exporting to a JSON lines file) to compare across geometries, mainly to illustrate the current shortcoming but also for testing in the future.

For the following hex pin:

Geant4 is correct:

And ORANGE adds internal boundaries:

[github-actions[bot]]

Test summary

 3 264 files   5 077 suites   3m 30s :stopwatch:  1 526 tests  1 498 :white_check_mark: 27 :zzz: 1 :x: 16 899 runs  16 831 :white_check_mark: 63 :zzz: 5 :x:

For more details on these failures, see this check.

Results for commit 009f574f.

[sethrj]

@elliottbiondo if your dives into g4/vg safety code show any weird approximations/inaccuracies, this would be a great way to test them. I don't think I have the bandwidth to fully generalize and integrate this at the moment though.

[sethrj]

Closing since this was a one-off experiment.