Add missing docstrings

[glenn-jocher]

🛠️ PR Summary

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🌟 Summary

Enhancements in documentation and testing for HUB SDK.

📊 Key Changes

• Added docstrings to classes and methods across multiple files for better code documentation.
• Implemented new tests for creating, retrieving, updating, listing, uploading, and deleting datasets, models, and projects using HUBClient.
• Decorators and helper functions now have descriptive comments to explain their use.

🎯 Purpose & Impact

• 📝 The added docstrings improve code readability and maintainability, making it easier for developers to understand the SDK's functionality.
• ✅ New tests increase the robustness of the SDK by ensuring key features work as expected, leading to fewer bugs and a more reliable product for users.
• 🧑‍💻 Clearer comments aid in onboarding new developers or contributors, streamlining the development process.