Description

This PR adds a simplified citability measure that looks for a CITATION.cff, CITATION.bib, or a sub-header in a README.md which includes "Citation" or "Citing". I think we could improve upon this with more complex checking, but I didn't want to advance on premature enhancements here before better understanding what we might encounter in the wider ecosystem.

Along the journey for this PR I also opted to enhance tests from #115 so we may rapidly test repository scenarios using a repo_setup utility function and parameterized tests.

Closes #107

What is the nature of your change?

• Content additions or updates (adds or updates content)
• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• Breaking change (these changes would cause existing functionality to not work as expected).

Checklist

Please ensure that all boxes are checked before indicating that this pull request is ready for review.

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• I have made corresponding changes to related documentation (outside of book content).
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• New and existing tests pass locally with my changes.
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