Belatedly address several review comments of my earlier PRs

[jhrozek]

Summary

We merged PRs to avoid blocking other work while the PRs still had some comments pending. This PR addresses them.

• Use named return values in parseArtifactName
• Add unit tests for artifact property handling
• Move WithSkipPrefixCheckTestOnly to tests

Change Type

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

make test

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[evankanderson]

LGTM, I like the added coverage, thank you!

[coveralls]

coverage: 53.133% (+0.3%) from 52.863%
when pulling 7343460 on jhrozek:review_comments
into b496555 on stacklok:main.