Fast service tier accepted; tool text outputs now serialized

Patch Changes

• 6157098: fix(openai): serialize tool text outputs when an output schema is configured
• 4cd4548: Accept serviceTier: 'fast' on OpenAI chat and responses models. OpenAI renamed priority processing to Fast mode and accepts service_tier: 'fast' and 'priority' interchangeably, so 'fast' is now passed through verbatim and gated on the same model capability as 'priority'.
• Updated dependencies [ad6a650]
• Updated dependencies [81cd026]
  • @ai-sdk/provider@4.0.7
  • @ai-sdk/provider-utils@5.0.25