Xtensor

[aprilnovak]

Description

Update OpenMC to xtensor v 0.26. Confirms this works with clang 19.1.7. This is necessary for many Cardinal users who rely on MOOSE's conda environment, which uses clang by default.

Fixes # 3183

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[aprilnovak]

I have clang-format v19 locally, but I'm not sure why the formatting check is failing (all changes are very simple changes to header paths)

[paulromano]

Thanks @aprilnovak for the PR. @jtramm and I have talked for a while about replacing xtensor with something internal for a variety of reasons, and I just learned today that he has been busy behind the scenes working on a replacement that is evidently nearly complete and is close to submitting a PR. So, let's wait for that to come in and hopefully that will resolve the issue with the latest clang compilers! 🤞

[aprilnovak]

Even better! Thanks @jtramm!