Convert CBECS processor to polars

[eringold]

Pull request overview

Converts CBECS processor from pandas to polars.

Pull Request Author

This pull request makes changes to (select all the apply):

• Postprocessing

Pull Request Author Checklist:

• Tagged the pull request with the appropriate label (documentation, infrastructure, sampling, workflow measure, upgrade measure, reporting measure, postprocessing) to help categorize changes in the release notes.

Pull Request Reviewer Checklist:

• Perform a code review on GitHub
• .yml and README.md files updated
• Author had ensured all modified and new functions have docstrings
• All changes have been implemented: data, methods, tests, documentation
• Measure tests written and adequately cover anticipated cases
• Run measure tests and ensure they pass
• New measure tests add to to test/reporting_measure_tests.txt, test/workflow_measure_tests.txt, or test/upgrade_measure_tests.txt
• Ensured code files contain License reference
• (when CI works) Confirm no additional rubocop errors
• Check edited measure .xml files updated
• (when CI works) CI status: all tests pass

• ComStock documentation adequately describes the new assumptions
• Reviewed change documentation, results differences are reasonable, and no new errors introduced
• Author has addressed comments in change documentation

ComStock Licensing Language - Add to Beginning of Each Code File

# ComStock™, Copyright (c) 2025 Alliance for Sustainable Energy, LLC. All rights reserved.
# See top level LICENSE.txt file for license terms.

[eringold]

existing (refactored) test passes, and I have an 'old vs new' test comparing each value from each col that also passes - happy to share for review.

[ChristopherCaradonna]

Did you run this end to end, and check that the resulting file is identical, including data types?

[ChristopherCaradonna]

Did you run this end to end, and check that the resulting file is identical, including data types?