Add a comprehensive endpoint latency testing system that allows users to:
- Test multiple API endpoints concurrently
- Auto-select the fastest endpoint based on latency
- Add/remove custom endpoints dynamically
- View latency results with color-coded indicators
Backend (Rust):
- Implement parallel HTTP HEAD requests with configurable timeout
- Handle various error scenarios (timeout, connection failure, invalid URL)
- Return structured latency data with status codes
Frontend (React):
- Create interactive speed test UI component with auto-sort by latency
- Support endpoint management (add/remove custom endpoints)
- Extract and update Codex base_url from TOML configuration
- Integrate with provider presets for default endpoint candidates
This feature improves user experience when selecting optimal API endpoints,
especially useful for users with multiple provider options or proxy setups.
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