Sourcegen CLib edge cases

[ischoegl]

Changes proposed in this pull request

Address several edge cases encountered in CLib

• Extend auto-generation of CLib APIs to variables (not just functions)
• Use ReactionPathDiagram as an example (also, C++ API is updated to match Python API)
• Expose Cantera constants to CLib
• Implement CLib loggers

If applicable, fill in the issue number this pull request is fixing

Addresses Cantera/enhancements#220

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

Attention: Patch coverage is 60.41667% with 19 lines in your changes missing coverage. Please review.

Project coverage is 74.39%. Comparing base (e6f3e9d) to head (bb81255).

Files with missing lines	Patch %	Lines
src/kinetics/ReactionPath.cpp	59.45%	12 Missing and 3 partials ⚠️
interfaces/cython/cantera/reactionpath.pyx	63.63%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1846      +/-   ##
==========================================
- Coverage   74.41%   74.39%   -0.02%     
==========================================
  Files         386      386              
  Lines       53628    53649      +21     
  Branches     9063     9069       +6     
==========================================
+ Hits        39905    39913       +8     
- Misses      10652    10662      +10     
- Partials     3071     3074       +3     

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