Fix Axisymmetric HLL

[ChrisZYJ]

Description

The current axisymmetric HLL simulations were incorrect. I fixed them by adding special treatment for the radial direction within the HLL solver. (The HLLC solver has always been correct.)

Also added a "Axisymmetric + HLL" test.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Something else

Scope

• This PR comprises a set of related changes with a common goal

How Has This Been Tested?

• HLLC Axisym (bottom) vs HLL Axisym Old (top- wrong)

animation.mp4

• HLLC Axisym (bottom) vs HLL Axisym New (top- corrected)

animation.mp4

• HLLC Axisym (bottom) vs HLLC 3D (top) [Note: both are correct and unchanged; for reference only]

animation.mp4

Checklist

• I have added comments for the new code
• I added Doxygen docstrings to the new code
• I have made corresponding changes to the documentation (docs/)
• I have added regression tests to the test suite so that people can verify in the future that the feature is behaving as expected
• I have added example cases in examples/ that demonstrate my new feature performing as expected.
  They run to completion and demonstrate "interesting physics"
• I ran ./mfc.sh format before committing my code
• New and existing tests pass locally with my changes, including with GPU capability enabled (both NVIDIA hardware with NVHPC compilers and AMD hardware with CRAY compilers) and disabled
• This PR does not introduce any repeated code (it follows the DRY principle)
• I cannot think of a way to condense this code and reduce any introduced additional line count

If your code changes any code source files (anything in src/simulation)

To make sure the code is performing as expected on GPU devices, I have:

• Checked that the code compiles using NVHPC compilers
• Checked that the code compiles using CRAY compilers
• Ran the code on either V100, A100, or H100 GPUs and ensured the new feature performed as expected (the GPU results match the CPU results)
• Ran the code on MI200+ GPUs and ensure the new features performed as expected (the GPU results match the CPU results)
• Enclosed the new feature via nvtx ranges so that they can be identified in profiles
• Ran a Nsight Systems profile using ./mfc.sh run XXXX --gpu -t simulation --nsys, and have attached the output file (.nsys-rep) and plain text results to this PR
• Ran an Omniperf profile using ./mfc.sh run XXXX --gpu -t simulation --omniperf, and have attached the output file and plain text results to this PR.
• Ran my code using various numbers of different GPUs (1, 2, and 8, for example) in parallel and made sure that the results scale similarly to what happens if you run without the new code/feature

[codecov]

Codecov Report

Attention: Patch coverage is 37.50000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 43.73%. Comparing base (6b3e012) to head (bc483c2).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/simulation/m_riemann_solvers.fpp	37.50%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #794      +/-   ##
==========================================
- Coverage   43.73%   43.73%   -0.01%     
==========================================
  Files          65       65              
  Lines       19042    19050       +8     
  Branches     2327     2328       +1     
==========================================
+ Hits         8328     8331       +3     
- Misses       9307     9311       +4     
- Partials     1407     1408       +1     

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