This commit includes several improvements:

1. Enhanced test coverage:
   - Added tests for combined netem and iptables usage
   - Added tests for extended netem features (duplicate, corrupt, etc.)
   - Added tests for global parameters and error handling
   - Added testing documentation for future contributors

2. Improved documentation:
   - Added examples of using combined nettools images
   - Created advanced network chaos documentation
   - Added diagram illustrating nettools architecture
   - Added examples for complex network degradation scenarios

3. Made tests more robust and environment-agnostic to ensure
   they run reliably across different systems and configurations