Improved dataset_stats() YAML checks

[glenn-jocher]

🛠️ PR Summary

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🌟 Summary

Improved code organization and enhanced dataset statistics functionality in YOLOv5 dataloaders.

📊 Key Changes

• 🧹 Code Cleanup: Comments have been updated to reflect the reorganization (utils.datasets -> utils.dataloaders).
• 🔍 Improving Dataset Unzipping: Added assertions to the _unzip function for better error handling and clarity.
• 🔄 Refactoring Helper Functions: Private function naming (prefixed with _) for utility functions such as _round_labels, _find_yaml, and _hub_ops.
• 🧐 Enhanced Dataset Stats: The dataset_stats function now includes assertions to ensure proper .yaml file finding and handling multiple .yaml files.

🎯 Purpose & Impact

• 🗂 Better Organization: Helps maintain clean codebase by correctly referencing the updated file structure, which is helpful for new contributors.
• 🛠 Error Handling Improvements: Makes unzipping more robust and error-proof, giving users clearer feedback if something goes wrong.
• 🚀 Function Clarity: The privatization of helper functions enforces better practice in code structure and usage.
• 📈 Detailed Stats: Provides users with more accurate and reliable dataset statistics, which is critical for data analysis and model performance understanding.

[glenn-jocher]

@kalenmike here are the dataset_stats() yaml check improvements I mentioned.