feat(core): add models and class for pycytominer core

[kenibrewer]

Description

This represents initial work toward an experimental core module that is intended to the basis of refactoring pycytominer towards a more modular and object oriented design.

What is the nature of your change?

• [ ] Bug fix (fixes an issue).
• [x] Enhancement (adds functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
• [x] This change requires a documentation update.

Checklist

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

• [ ] I have read the CONTRIBUTING.md guidelines.
• [ ] My code follows the style guidelines of this project.
• [ ] I have performed a self-review of my own code.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have made corresponding changes to the documentation.
• [ ] My changes generate no new warnings.
• [ ] New and existing unit tests pass locally with my changes.
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have deleted all non-relevant text in this pull request template.

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📚 Documentation preview 📚: https://pycytominer--383.org.readthedocs.build/en/383/