Close [AI-125](https://linear.app/affine-design/issue/AI-125)
What Changed?
- Add `gemini-2.5-flash-preview-04-17` model
- Add `thinkingConfig` provider options
- Add callout syntax highlighting
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Added support for the "Gemini 2.5 Flash" model and updated the "Gemini 2.5 Pro" model to a newer version.
- Enhanced streaming responses to better format reasoning outputs and provide clearer callouts in AI-generated content.
- **Bug Fixes**
- Improved audio transcription prompts in test cases for more accurate and explicit testing.
- **Documentation**
- Expanded citation instructions for AI chat responses, including examples for multiple citations.
- **Chores**
- Updated the "@ai-sdk/google" dependency to a newer version.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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