Add support for MiniMax M2.5 series models via OpenAI-compatible API:
- Add minimax_fn() to Provider class with configurable base URL
- Support both international and China mainland endpoints
- Update documentation in README.md and README_CHS.md
- Add MINIMAX_API_KEY and MINIMAX_BASE_URL to .env.example
- Add unit tests for MiniMax provider
Made-with: Cursor
