Bugfix #2762 PCPCombine derive field info

[georgemccabe]

Pull Request Testing

• Describe testing already performed for these changes:
  

Modified unit test to use expected format for derive mode commands, then made sure test ran successfully after code changes

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

Ensure use case described in #2752 that could not run specifying the full valid time YYYYMMDD_HHMMSS as the field info now works as expected.

• 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]
  
  If yes, please describe:

• Please complete this pull request review by 11/1/2024.
  

Pull Request Checklist

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[CPKalb]

I tested these changes and PCP-Combine ran as expected. The output matched what it should look like.