Replace defunct test description links with test sandbox in notebooks

[nrichers]

What and why?

Notebook links that pointed at removed text-only test description pages now point at the production test sandbox documentation instead, so readers following quickstart, validation, and use-case notebooks land on the current docs surface.

Before: Relative or legacy links to defunct per-test description pages.

After: Links to the interactive test sandbox guide where appropriate across eight notebooks.

How to test

• Open the changed notebooks and follow updated documentation links; confirm they resolve on the docs site to the test sandbox page.
• Run quarto preview (or your usual docs build) if these notebooks are rendered as part of the site and verify links are not broken.

What needs special review?

• Spot-check that each replaced link is the right destination (test sandbox vs. another guide) for the surrounding notebook context.
• Confirm no customer-facing notebook still references removed test-description paths.

Dependencies, breaking changes, and deployment notes

• None. Documentation-only notebook link updates in validmind-library.

Release notes

internal — Notebook link maintenance only; no product behavior change.

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]

PR Summary

This pull request refines several Jupyter notebooks by updating the documentation that explains how to run and interpret various tests. The main changes involve removing markdown hyperlinks from test names (e.g., ClassifierPerformance, ROCCurve, HighPearsonCorrelation, etc.) in favor of plain text references. Additionally, the pull request standardizes trailing newline characters for a more consistent presenting style. These changes do not alter any test functionality but instead improve the readability and consistency of the instructions provided to users.

In essence, the update:

• Replaces embedded markdown links with plain text for ease of reading.
• Includes formatting adjustments, such as appending newline characters uniformly at the end of instruction lines.
• Clarifies the description of test procedures, ensuring that users can follow the instructions without being distracted by hyperlinks.

Test Suggestions

• Render the updated notebooks to verify that all markdown formatting appears consistent and as expected.
• Manually review the instructional text to ensure that the removal of hyperlinks does not impact user comprehension.
• Run a sample workflow with the affected tests to confirm that functionality remains unchanged.