Fix for nuclear speckle image display in CytoDataFrame

[d33bs]

Description

This PR adds fixes for bugs exhibited for nuclear speckle image data through CytoDataFrames. I found that this had to do with first a bounding box reference error (bounding box column references were static), and then second an image rendering issue (where images would not render correctly with the existing code). I made changes to these areas and added a new module for image-specific work to keep the CytoDataFrame class lean.

Along the way I found that cv2 causes an error with coverage and added a fix for this. I also added a fix to how the coverage badge renders for PyPI display (relative links don't display properly).

Thanks for any feedback you may have!

Closes #62

What kind of change(s) are included?

• Feature (adds or updates new capabilities)
• 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.

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

[jenna-tomkinson]

LGTM! I am excited that this is so close to being ready!

[d33bs]

Thanks @jenna-tomkinson for the review! Merging this in after addressing the comments.