Add ClassificationModel TF export assert

[glenn-jocher]

Export to TF not yet supported, warning alerts users.

Signed-off-by: Glenn Jocher glenn.jocher@ultralytics.com

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhancements to the export functionality of YOLOv5 models with explicit support for detection models.

📊 Key Changes

• 🔄 Changed import in export.py to include ClassificationModel along with Detect.
• ✅ Added assertion to prevent the export of ClassificationModel to TensorFlow formats, as this is not yet supported.

🎯 Purpose & Impact

• 💡 The purpose of these changes is to prepare the code base for future ClassificationModel support while maintaining stability.
• 🔍 By adding an assertion, users are clearly informed that exporting classification models to TensorFlow formats is currently unavailable, preventing confusion or errors.
• 🛠️ The impact for users is minimal at this stage, as it’s mainly a preventive measure, but it sets the stage for smoother expansions to model export capabilities in upcoming versions.

[glenn-jocher]

@AyushExel I'm adding a warning here on export.py to alert users that ClassificatioModels are not TF export supported yet.