Build NCrystal from Source for OpenMC

[ahnaf-tahmid-chowdhury]

Description

This PR modifies the OpenMC build process to compile NCrystal from source instead of relying on the manylinux-provided package. The motivation behind this change is to ensure a more streamlined integration, avoiding unnecessary dependencies and improving compatibility.

Motivation

• Using the manylinux version results in a dependency on libNCrystal.so, which is dynamically loaded via subprocess, adding inefficiencies.

• Setting LD_LIBRARY_PATH is an option, but it introduces complexity.

Reference

This PR follows up on discussions in another PR (shimwell/openmc/pull/67), where the issue of dependency management was raised. As suggested, this change is being made separately to integrate source-built NCrystal before addressing packaging concerns.

[shimwell]

Many thanks for making this PR @ahnaf-tahmid-chowdhury

This would be very enabling for the sci kit core wheel building.

@tkittel perhaps has some comments on this

[tkittel]

Yes, I have some comments. On vacation and busy with kids right now, but will try to find time a bit later :-)

[ahnaf-tahmid-chowdhury]

It seems that ncrystal-python requires ncrystal-core to be installed; otherwise, it is broken. We need to install the full ncrystal package.

How would you like to proceed? We can either make ncrystal a runtime dependency, or create a fallback so users can install ncrystal when it's called but not installed, also add an optional dependency on pyproject.toml file.