Single cache_version definition

[glenn-jocher]

Defines dataset labels *.cache version in a single place, fixing a bug introduced in #4845.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Updated dataset caching logic in YOLOv5 for improved consistency and maintainability.

📊 Key Changes

• Introduced cache_version variable in LoadImagesAndLabels class.
• Updated cache validation to check against the cache_version variable.
• Ensured cache version and file hash checks match current dataset.

🎯 Purpose & Impact

• Purpose: The changes simplify the process of ensuring the cache format remains consistent across versions, making maintenance easier and reducing potential errors caused by format discrepancies.
• Impact: Users will benefit from more consistent cache behavior when training or evaluating models. It will minimize issues related to outdated or mismatched cache data, leading to a smoother user experience. 🔄💾