docs: add airtbench dataset readme

[GangGreenTemperTatum]

external AIRTBench dataset README v1.0

Key Changes:

• adds external AIRTBench dataset README v1.0

Added:

• adds external AIRTBench dataset README v1.0

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Generated Summary:

• Updated the README to reflect the external release of the AIRTBench dataset.
• Added comprehensive sections including Overview, Dataset Statistics, and Model Success Rates.
• Introduced a detailed Data Dictionary outlining identifiers, primary outcomes, performance metrics, resource usage, cost analysis, conversation content, and error analysis.
• Provided multiple usage examples covering basic analysis, cost analysis, performance analysis, and conversation content extraction.
• Included version history and contact information for dataset support.

This summary was generated with ❤️ by rigging

[linear]

ENG-2185 data: upload dataset to `AIRTBench-Code` repository with `README`

https://github.com/dreadnode/AIRTBench-Code/dataset/README.md