fix: remove stream_options from xAI provider to fix Grok 4 API errors

[roomote]

Summary

This PR fixes API errors that occur when using the Grok 4 model by removing the stream_options parameter from the xAI provider.

Problem

Users reported that while Grok 3 works well, Grok 4 frequently encounters API errors that make it difficult to complete tasks. The issue was that the xAI provider was including stream_options: { include_usage: true } in API requests, but Grok models do not support this parameter.

Solution

• Removed stream_options: { include_usage: true } from the XAIHandler.createMessage() method
• Added a comment explaining that Grok models don't support the stream_options parameter
• Updated the corresponding test to reflect this change

Testing

• All xAI provider tests pass successfully
• Linting and type checking pass

Related Issue

Fixes #6211

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Important

Remove stream_options from XAIHandler.createMessage() to fix Grok 4 API errors and update tests accordingly.

• Behavior:
  • Removed stream_options: { include_usage: true } from XAIHandler.createMessage() in xai.ts to fix Grok 4 API errors.
  • Added a comment in xai.ts explaining Grok models don't support stream_options.
• Testing:
  • Updated test in xai.spec.ts to reflect removal of stream_options parameter.
  • All xAI provider tests pass successfully.

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[daniel-lxs]

The issue is not properly scoped so this is most likely incorrect