Fix GPU build and add NVHPC CI

[JCGoran]

This PR does a couple of things:

• fixes the build so NEURON compiles and runs under NVHPC
• modifies the tests so that some have more relaxed accuracy thresholds on NVHPC, while others are disabled (notably, the LFP test segfaults)
• adds a CI that runs on a custom runner, which has the necessary software and hardware to build and run NEURON under NVHPC (i.e. with GPU capabilities). The underlying runner is a Ubuntu 24.04 LTS container with an NVIDIA GPU.

With the above, as long as the custom runner is available, we will always be certain that NEURON successfully builds and runs with its GPU features enabled.

Note that the documentation detailing how to setup the runner is available in this repo (only accessible to org members).

[azure-pipelines]

✔️ 02e96d0 -> Azure artifacts URL

[github-actions]

✔️ b315bcb -> artifacts URL

[sonarqubecloud]

Please retry analysis of this Pull-Request directly on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.55%. Comparing base (81b99c0) to head (4786493).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3607      +/-   ##
==========================================
+ Coverage   68.52%   68.55%   +0.02%     
==========================================
  Files         686      686              
  Lines      116776   116779       +3     
==========================================
+ Hits        80018    80053      +35     
+ Misses      36758    36726      -32     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[azure-pipelines]

✔️ 4786493 -> Azure artifacts URL

[github-actions]

✔️ 02e96d0 -> artifacts URL

[github-actions]

✔️ 4786493 -> artifacts URL