Feature #2742 main_v5.1 fix StatAnalysis to set fcst_lev/obs_lev

[georgemccabe]

instead of fcst_level/obs_level to match actual MET config variable names. Added unit tests to ensure correct behavior occurs

Pull Request Testing

• Describe testing already performed for these changes:
  

Added tests then fixed the code to make them pass

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

Review code changes, ensure all automated tests pass

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [Yes]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Do these changes introduce new SonarQube findings? [No]
  
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• Please complete this pull request review by 11/1/2024.
  

Pull Request Checklist

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• Add any new Python packages to the METplus Components Python Requirements table.
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