Replace defunct test description links with test sandbox in notebooks

[nrichers]

Pull Request Description

What and why?

Several notebooks still linked to retired test description pages. Those references are updated to use the beta test sandbox instead, so readers land on the current way to explore and run tests. The behavior for running code in the notebooks is unchanged apart from navigation and documentation links.

How to test

• Open any of the modified notebooks under notebooks/ and confirm links that previously pointed at defunct test descriptions now point at the test sandbox (or the intended replacement target).
• Optional: run cells that only print or follow links to confirm URLs resolve in your environment.

What needs special review?

Confirmation that each replacement link matches the surrounding context (comparison tests, raw data, quickstart, tutorials, and use-case notebooks).

Dependencies, breaking changes, and deployment notes

• None.
• No deployment steps required.

Release notes

documentation — Notebook learning paths now point readers to the interactive ValidMind test sandbox instead of removed test catalog description links.

Checklist

• What and why
• Screenshots or videos (Frontend)
• How to test
• What needs special review
• Dependencies, breaking changes, and deployment notes
• Labels applied
• PR linked to Shortcut
• Unit tests added (Backend)
• Tested locally
• Documentation updated (if required)
• Environment variable additions/changes documented (if required)

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[github-actions]

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[validbeck]

Looks good, but I moved some notebooks for PRT around so some gnarly merge conflicts need to be resolved.

[github-actions]

PR Summary

This PR refines the documentation across multiple Jupyter notebooks by replacing embedded markdown links with plain text names for tests. The changes remove URL wrappers from test names (e.g., converting "ClassifierPerformance" to "ClassifierPerformance") and ensure that appropriate newline characters are added at the end of text snippets. These modifications improve readability and consistency in the instructional content without affecting any underlying functional code. The updates span instructions for running classifier performance tests, ROC curve tests, class imbalance tests, Pearson correlation tests, and similar validations, thereby streamlining the presentation of the documentation and ensuring users have a clearer guide.

Test Suggestions

• Render the updated notebooks in Jupyter to verify that newline formatting and text rendering meet expectations.
• Manually verify that all test instructions display the intended plain text for test names without broken links.
• Run the notebooks to ensure that no functionality is inadvertently affected by documentation changes.