Map tool choice 'required' to 'auto' for Together

[Aaron1011]

Together doesn't mention supporting 'required' in its docs, and attempting to pass it in gives a generic 'Invalid request' error. This fixes a Together tool-calling test when running without the provider-proxy cache

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Important

Maps tool_choice="required" to tool_choice="auto" in TogetherRequest to prevent errors with Together API.

• Behavior:
  • Maps tool_choice="required" to tool_choice="auto" in TogetherRequest to avoid 'Invalid request' error from Together API.
• Files:
  • Modifies together.rs to implement the mapping logic in TogetherRequest::new() function.

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[Copilot]

Pull Request Overview

This PR fixes a compatibility issue between TensorZero and the Together AI provider by mapping the unsupported 'required' tool choice to 'auto'. Together AI doesn't support the 'required' tool choice option in their API, which was causing generic 'Invalid request' errors during tool-calling operations.

• Maps 'required' tool choice to 'auto' for Together AI provider compatibility
• Adds import for OpenAIToolChoiceString to support the mapping logic