Add Tuning Engines model provider sample

[cerebrixos]

Summary

• add a Tuning Engines OpenAI-compatible model provider sample for OpenAI Agents SDK workflows
• add worker and workflow runner scripts using TUNING_ENGINES_API_KEY, TUNING_ENGINES_MODEL, and TUNING_ENGINES_BASE_URL
• update the model providers README with setup instructions

Validation

• git diff --check
• python3 -m compileall openai_agents/model_providers

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All committers have signed the CLA.

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[cerebrixos]

Updated this branch on top of current main (4d453de). The rebase was clean.

Validation: git diff --check upstream/main...HEAD passes.

[cerebrixos]

Hello team @mnichols . Please do consider this PR for merge. So much appreciate in advance :)

[jssmith]

@cerebrixos - we encourage you to consider developing a Temporal plugin and submitting it for distribution through Temporal's AI Partner Program. We cannot accept this sample PR.

[cerebrixos]

Thanks, @jssmith. Appreciate the clear direction. That makes sense; we will stop trying to land this as a samples-python contribution and build this as a Temporal plugin instead, then follow the Temporal AI Partner Program path for distribution. Thanks again for pointing us to the right channel.