Context manager open(file) as f fixes

[glenn-jocher]

Possible fix for #7288

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced file handling for better resource management in yolov5.

📊 Key Changes

• Updated VOC.yaml to use a context manager for reading image ids.
• Modified export.py to use a context manager when reading and rewriting JSON files.
• Refactored models/common.py to parse GraphDef with a context manager.
• Changed example_request.py in flask_rest_api to read image data within a context manager.
• Small comment update in restapi.py, possibly for better documentation clarity.

🎯 Purpose & Impact

• Improved Code Reliability: Using context managers (with statement) ensures files are properly closed after operations, reducing the likelihood of file handle leaks.
• Resource Efficiency: This is a more resource-efficient way of handling files, which can slightly improve the performance of the system and avoid potential bugs in the long run.
• Maintainability: These changes make the code more explicit and Pythonic, which is generally easier to read and maintain.