refactor: replace all Chinese comments with English

Removed all Chinese documentation and comments from:
- AsyncToolCallback.java
- ToolExecutionMode.java

All comments now follow Spring project conventions:
- Professional English technical writing
- Clear and concise javadoc
- Proper formatting and structure
- Consistent terminology

These changes ensure:
✅ International collaboration readiness
✅ Spring framework compliance
✅ Professional code documentation standards

Signed-off-by: Spring AI Contributor <contributor@example.com>

Author: JGoP-L