feat: add memory warnings and improve build instructions in dynamo_check.py

- Add ⚠️ warning symbols when OS/GPU memory usage reaches 90%+
- Include safe error handling for memory percentage calculations
- Replace dynamo_build.sh dependency with detailed development vs. production build commands
- Development mode: Fast debug builds with editable installation
- Production mode: Optimized release builds with wheel packages
- Add immediate testing option via PYTHONPATH without rebuilding
- Improve build workflow documentation and troubleshooting guidance

Author: keivenchang