sphinx-multiversion was not working correctly in that it:

• did not use the appropriate dependencies for each version of pyremap
• did not reinstall pyremap when it checked out a new version of pyremap, causing issues with the auto-generated API

This merge removes sphinx-multiversion and instead adopts a custom version dropdown developed with help form ChatGPT.

For now at least, the version dropdown will only be available in main and future releases of MPAS-tools (though we could back-port the dropdown and rebuild older versions of the docs if desired).

This pull request includes several changes focused on improving the documentation build process and enhancing the versioning system for the mpas_tools package. The most important changes include replacing sphinx-multiversion with a custom versioning solution, updating the documentation build commands, and adding a version switcher to the documentation.

Documentation Build Process Improvements:

• .github/workflows/docs_workflow.yml: Updated the documentation build command to use a custom versioning solution and ensured that only the latest changes are applied to the documentation for the current branch.
• conda_package/dev-spec.txt: Removed sphinx-multiversion from the dependencies.
• conda_package/docs/Makefile: Added targets for building versioned HTML and cleaning versioned HTML builds.
• conda_package/docs/conf.py: Removed sphinx-multiversion related configurations and added a context for the current documentation version. [1] [2]

Version Switcher Implementation:

• conda_package/docs/_templates/layout.html: Added meta tags and a script to create a version switcher container in the documentation sidebar.
• conda_package/docs/shared/version-switcher.js: Implemented a JavaScript file to dynamically load and display available documentation versions.
• conda_package/docs/_static/style.css: Styled the version switcher dropdown menu.

Documentation Content Updates:

• conda_package/docs/building_docs.rst: Updated instructions for building and previewing the documentation locally.
• conda_package/docs/index.rst: Added new sections to the table of contents for visualization tools.
• conda_package/docs/making_changes.rst: Removed outdated instructions for adding new versions to the documentation.

Miscellaneous Changes:

• conda_package/docs/generate_versions_json.py: Added a script to generate a versions.json file for the version switcher.
• conda_package/mpas_tools/ocean/viz/transect/__init__.py: Added a missing import for interp_mpas_to_transect_cells.