fix: correct key names to match server

[kalenmike]

This PR corrects the key names for the response returned by the server.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced model property checks in the hub-sdk.

📊 Key Changes

• Changed the is_resumable method to check for has_last_weights instead of checking the status for "training".
• Updated the has_best_weights method to directly check a new flag has_best_weights rather than deriving from other properties.
• Standardized boolean property names in is_pretrained and is_custom methods to is_pretrained and is_custom for consistency.

🎯 Purpose & Impact

• 🛠️ Improved Consistency: Property names and checks are now more consistent and self-descriptive, reducing confusion.
• ⏩ Efficient Checks: Direct property checks may improve efficiency when querying model states.
• 🧑‍💻 Better Developer Experience: Clearer property names can help developers understand the SDK capabilities faster.
• 📈 Potential for More Accurate Model State Reporting: By using more explicit flags, models' states might be represented more accurately in the hub.