Fix is_writeable() for 3 OS support

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced the configuration directory handling and write permission checking for better cross-platform support.

📊 Key Changes

• 📁 Updated user_config_dir to determine user-specific configuration directory with improved logic.
• 🛠 Fixed an issue with is_writeable, which now robustly checks for write permissions through a test file creation method.

🎯 Purpose & Impact

• 🚀 Purpose: To ensure that the application can correctly locate and use the configuration directory regardless of the operating system and environment constraints (like Google Cloud Functions or AWS Lambda).
• 💾 Impact: Users across different platforms should experience more reliable behavior when the software attempts to read or write configurations, with reduced chance of permissions-related errors.
• 🔒 Security and Stability: The new approach in getting the write permissions helps to avoid known issues on Windows, thereby increasing security and stability for all users.