Add GitHub citation file (CITATION.cff)

[Copilot]

Description

This PR adds a CITATION.cff file to the repository, following the guidance from the GitHub documentation on citation files and reproducing the work done in astronomy-commons/lsdb#594.

What is CITATION.cff?

The Citation File Format (CFF) is a standard format for providing citation metadata for software. When a CITATION.cff file is present in a repository, GitHub automatically displays a "Cite this repository" button, making it easy for users to properly cite the software in their research and publications.

Changes Made

• Added CITATION.cff to the repository root with the following metadata:
  • Project title and description
  • Authors (LINCC Frameworks)
  • Repository and documentation URLs
  • License information (MIT)
  • Relevant keywords (pandas, astronomy, time-domain, nested-data, python)

Benefits

• Users can easily cite nested-pandas in their research
• Citations can be exported in multiple formats (BibTeX, APA, EndNote, RIS, etc.)
• Improves software discoverability and proper attribution
• Follows best practices from similar astronomy projects (e.g., Astropy)

Validation

The CITATION.cff file has been validated using the official cffconvert tool and meets the CFF specification version 1.2.0.

Closes #[issue_number]

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• docs.github.com
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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add github citation file</issue_title>
<issue_description>Reproduce the work in astronomy-commons/lsdb#594 for this repository, following the guidance here: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #204

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.77%. Comparing base (c5cf5ee) to head (1f2df5f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #383   +/-   ##
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  Coverage   97.77%   97.77%           
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  Files          19       19           
  Lines        2024     2024           
=======================================
  Hits         1979     1979           
  Misses         45       45           

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