Enhance streaming response handling and VTC processing

- Improve VTC response wrapper with better XML tool call detection and buffering
- Enhance streaming response adapters with comprehensive SSE handling
- Add robust usage calculation and token tracking for streaming responses
- Implement improved error handling and async stream management
- Add support for tool call buffering and multiline XML tag processing

These changes improve the reliability and functionality of streaming responses,
particularly for VTC (Virtual Tool Calling) scenarios with XML-based tool calls.

Author: Mateusz