[RFC]: add support for navigating to the "next" and "previous" package

[kgryte]

Description

This RFC proposes adding support for navigating to the "next" and "previous" package.

While packages do not have an inherent order, allowing easier navigation between packages allows users to explore the project more readily.

The concept of navigating to the "next" and "previous" API is found elsewhere (e.g., see NumPy's sin).

This should be a straightforward addition. Will require loading a list of packages and tracking the index of the currently active package within that list.

Related Issues

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Questions

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Other

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Checklist

• [X] I have read and understood the Code of Conduct.
• [X] Searched for existing issues and pull requests.
• [X] The issue name begins with RFC:.

[kgryte]

This now implemented and deployed.