Add HDF5 + XDMF output module

[SpeedyTurtle599]

Description

Adds a new module m_hdf5_xdmf_output to provide native HDF5 and XDMF output support for MFC without third-party Silo dependency. Implements functions for initializing HDF5, writing grid and variable data, and generating XDMF metadata.

Type of change

• New feature (non-breaking change which adds functionality)

Scope

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

How Has This Been Tested?

• Test A
• Test B

Test Configuration:

Test system details: M3 Max MacBook Pro, macOS 26.2, MFC built from source (not Homebrew)
Compilers: GNU 15.2 suite (gcc, g++, gfortran), OpenMPI 5

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 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

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[SpeedyTurtle599]

oops...will remove

[sbryngelson]

Please add documentation. Aside from the usual documentation we do, it would be useful to have a "guide" on how and when to use different I/O options.

[codecov]

Codecov Report

❌ Patch coverage is 1.56250% with 189 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.58%. Comparing base (df782b5) to head (5d7ebef).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/post_process/m_hdf5_xdmf_output.fpp	0.00%	171 Missing ⚠️
src/post_process/m_data_output.fpp	10.00%	16 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1101      +/-   ##
==========================================
- Coverage   43.98%   43.58%   -0.40%     
==========================================
  Files          71       72       +1     
  Lines       20284    20476     +192     
  Branches     1982     2000      +18     
==========================================
+ Hits         8922     8925       +3     
- Misses      10225    10412     +187     
- Partials     1137     1139       +2     

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