Fix Python sdist issues

[speth]

Changes proposed in this pull request

• Fix installation of YAML data files in the Python sdist
• Simplify command line interface for building the sdist
• Speed up CI by using micromamba
• Remove test code from coverage report to avoid inflating apparent coverage

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

Resolves #1678.

If applicable, provide an example illustrating new features this pull request is introducing

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 72.82%. Comparing base (4565a55) to head (e0654b2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1708      +/-   ##
==========================================
- Coverage   75.72%   72.82%   -2.90%     
==========================================
  Files         443      379      -64     
  Lines       60981    53592    -7389     
  Branches     9557     9122     -435     
==========================================
- Hits        46178    39031    -7147     
+ Misses      11777    11610     -167     
+ Partials     3026     2951      -75     

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