[Aaqibhafeezkhan]

What changed

• Add a pytest smoke-test harness that discovers Python code blocks in explainers/*.md marked with # runnable and executes them in isolated subprocesses from the repository root.
• Include the explainer filename and code-block number in failure messages, with execution timeouts and support for the existing slow pytest marker through an optional # slow directive.
• Mark the predictive-parity example as runnable and add a self-contained pandas sample to exercise predictive_parity_gap and base_rate_gap.
• Document how to mark runnable examples, configure slow examples, and keep snippets self-contained in CONTRIBUTING.md.

Closes #1098

[vercel]

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[github-actions]

@yakew7 @Shreyash0712 @ahmdkaml - new PR touching a path you own, please review.