Support [AI-82](https://linear.app/affine-design/issue/AI-82).
Added a `TextStreamParser` class to standardize formatting of different types of AI stream chunks across providers.
### What changed?
- Created a new `TextStreamParser` class in `utils.ts` that handles formatting of various chunk types (text-delta, reasoning, tool-call, tool-result, error)
- Refactored the Anthropic, Gemini, and OpenAI providers to use this shared parser instead of duplicating formatting logic
- Added comprehensive tests for the new `TextStreamParser` class, including tests for individual chunk types and sequences of chunks
- Defined a common `AITools` type to standardize tool interfaces across providers
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Enhanced formatting and structure for streamed AI responses, including improved handling of callouts, web search, and web crawl results.
- **Refactor**
- Streamlined and unified the processing of streamed AI response chunks across providers for more consistent output.
- **Bug Fixes**
- Improved error handling and display for streamed responses.
- **Tests**
- Added comprehensive tests to ensure correct formatting and handling of various streamed message types.
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