Summary by cubic

Added provider options to ChatVercel to control Vercel AI Gateway routing and fallback order. Also improved handling for Anthropic models and updated docs and examples.

• New Features
  • Added provider_options to ChatVercel; passed as extra_body.providerOptions.
  • Supports gateway routing order (e.g., ['vertex', 'anthropic']).
  • Anthropic models now follow the optimized structured-output path.
  • Updated docs and example to show basic and provider-order usage.

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