add workflow for nvhpc testing

[rem1776]

Description
adds a workflow for testing with nvhpc compilers. Instead of using a container image like the other workflows, this will use spack to build the compiler, then save it to a spack OCI build cache for subsequent runs.

The package versions will be determined by the latest software available in the packages_ref option, which corresponds to the latest tag in the spack-packages repo. This prevents frequent rebuilds due to changing hashes by using a stable package list, but will need to updated.

needs #1873 merged first since that fixes the compilation error.

How Has This Been Tested?
tested on my fork with my package registry:
https://github.com/rem1776/FMS/actions/runs/26187563194/job/77047118521

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes