Add nuclear speckles data with tests

[d33bs]

Description

This PR adds a subset of data focused on nuclear speckles from a collaboration between the Way Lab and Alexander Lab. The data was used as inspiration for image-based adjustments within CytoDataFrame. I've added tests to help increase the coverage for the project and the data for other work as needed.

Thanks for any feedback you may have!

Closes WayScience/coSMicQC#66

What kind of change(s) are included?

• [ ] Documentation (changes docs or other related content)
• [ ] Bug fix (fixes an issue).
• [x] 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.

• [x] I have read and followed the CONTRIBUTING.md guidelines.
• [x] I have searched for existing content to ensure this is not a duplicate.
• [x] I have performed a self-review of these additions (including spelling, grammar, and related).
• [x] These changes pass all pre-commit checks.
• [x] I have added comments to my code to help provide understanding
• [x] I have added a test which covers the code changes found within this PR
• [x] I have deleted all non-relevant text in this pull request template.

[d33bs]

Thanks @jenna-tomkinson, merging this in!