Add citation metadata (CITATION.cff, .zenodo.json) to support scholarly use

[cvanelteren]

This PR formally introduces citation metadata for the UltraPlot project.

UltraPlot is a continuation of the original ProPlot library, which has not seen active development since 2022. While ProPlot laid the foundation for many of the ideas in UltraPlot, this project has been significantly restructured, modernized, and extended, and is being actively maintained.

To acknowledge this transition and to support reproducible and citable scientific software, we now include:

• A CITATION.cff file for automatic citation support on GitHub and with Zotero.
• A .zenodo.json file for future DOI integration via Zenodo.
• A BibTeX citation in the README for easy copy-paste into academic manuscripts.

We are committed to maintaining this project as a reliable and actively supported plotting library, especially for scientific users. We encourage users to cite UltraPlot if it contributes to their research. The citation metadata also acknowledges prior work from ProPlot and Matplotlib, on which UltraPlot is based.

Example Citation (BibTeX)

@software{vanElteren2025,
  author       = {Casper van Elteren and Matthew Becker},
  title        = {UltraPlot: A succinct wrapper for Matplotlib},
  year         = {2025},
  version      = {1.5.7},
  publisher    = {GitHub},
  url          = {https://github.com/Ultraplot/UltraPlot}
}

We believe clear authorship and citation support are essential to long-term sustainability in scientific software.

Please check if I added your affiliation correctly @beckermr. Will need to update the zenodo links if the format is accepted as is.

[beckermr]

Needs a DOI but otherwise LGTM.

[beckermr]

@cvanelteren See this link for integrating w/ zenodo via github to get a DOI: https://docs.github.com/en/repositories/archiving-a-github-repository/referencing-and-citing-content

[cvanelteren]

Will have a look an obtain the DOI