docs: add chaos testing example script

[ybdarrenwang]

Description

Adds documentation and example for the chaos testing module in Strands Evals.

The example demonstrates:

• Defining named effect maps (dict[str, dict[str, list[ChaosEffect]]]) for readable failure conditions (e.g., "search_timeout", "total_chaos")
• Using ChaosCase.expand(cases, effect_maps) to generate the Cartesian product of test cases × failure conditions with optional baseline
• Running a ChaosExperiment with ChaosPlugin for transparent fault injection
• Evaluating agent resilience with GoalSuccessRateEvaluator

The example uses ToolSimulator for reproducible tool responses and covers pre-hook effects (tool call failures), post-hook effects (response corruption), and compound multi-tool chaos.

Related Issues

#114

Type of Change

• New content

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using npm run dev
• Links in the documentation are valid and working

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