Debug optical boundary crossing

[hhollenb]

While working on implementing optical boundary crossing, I've encountered some failing tests for the optical PrimaryGenerator based on vecgeom + g4 versus orange + geant4. The vecgeom builds have slightly less step counters, and sometimes different step iterators than the orange + geant4 version.

This branch isolates some of the recent changes (e.g. vecgeom normals, optical surface physics) so that it's just moving photons across a surface with no other physics involved.

Closes #2041

[github-actions]

Test summary

 4 953 files   7 878 suites   16m 20s ⏱️
 2 034 tests  2 005 ✅ 24 💤  5 ❌
27 877 runs  27 745 ✅ 99 💤 33 ❌

For more details on these failures, see this check.

Results for commit 4f08d53.

♻️ This comment has been updated with latest results.

[amandalund]

Were the differences you were seeing in the docker build? The primary generator test results here look consistent, though for orange I think that test was only run with the single precision build, which doesn't check the number of steps or step iterations.

[hhollenb]

I'm seeing build errors in some of the build-spack tests: https://github.com/celeritas-project/celeritas/actions/runs/18468836404/job/52618665145?pr=2038#step:17:599

I've been comparing against some of the build-docker test failures as well, which build with orange and don't have these failures. I can move the PR out of drafts to run those as well

[amandalund]

I think that test is failing in the same way at least in the spack build tests (we "continue on error" for vecgeom-g4 with Geant4 versions less than 11.0, so unfortunately the tests with earlier Geant4 versions were failing as well even though it looks like they pass).

[hhollenb]

Gotcha, thanks for the heads up that's helpful to know!

Doing some more testing I found that the optical models were getting override in the LArSphereBase test, and after some searching it looks like only the Rayleigh model is causing the discrepancy. I know the inputs for that model got refactored a bit so I'll check that code next.