Improve test coverage of transport calculations and fix related bugs

[speth]

Changes proposed in this pull request

• Fix spatial scaling in MultiTransport::getMassFluxes and MultiTransport::getMolarFluxes
• Fix handling of actual versus reduced temperature when setting fits to collision integrals
• Ensure recalculation of properties after changes to transport polynomial fits
• Add bounds checks when accessing transport polynomial fits
• Move mixGasTransport and multiGasTransport tests to GTest suite
• Add various tests to improve coverage of transport-related code
• Remove some unnecessary error checking

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

All modified and coverable lines are covered by tests ✅

Project coverage is 73.54%. Comparing base (80c0bb2) to head (ec1dd12).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1825      +/-   ##
==========================================
+ Coverage   73.23%   73.54%   +0.30%     
==========================================
  Files         383      383              
  Lines       54652    54653       +1     
  Branches     9109     9105       -4     
==========================================
+ Hits        40027    40197     +170     
+ Misses      11612    11458     -154     
+ Partials     3013     2998      -15     

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[ischoegl]

@speth ... while I realize that this is work-in-progress, I have one minor comment.

[ischoegl]

Thanks, @speth, this all looks good to me!