Enhance Mistral: Improved Test Coverage, Code Optimization, and Bug Fixes

[YanSte]

1. Improved Test Coverage:

   • Increased overall test coverage from 80% to 94.82%.

2. Code Optimization:

   • Simplified complex logic for better readability and maintainability.
   • Removed unused and redundant code to streamline the codebase.

3. Bug Fixes:

   • Resolved the issue with double chunk handling to prevent duplication.

4. Enhancements:

   • Added test retry on stream.