ensure DockerNotebookSandbox checks image existence

[alcholiclg]

Change Summary

1. ensure DockerNotebookSandbox checks image existence and triggers Docker index refresh.
2. add temp to gitignore.

[gemini-code-assist]

Summary of Changes

Hello @alcholiclg, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Docker notebook sandbox environment by adding a check for Docker image existence, which improves robustness and provides better error feedback. It also updates the .gitignore file to exclude a temporary directory.

Highlights

• Docker Image Existence Check: Ensures that the DockerNotebookSandbox checks for the existence of a specified Docker image before attempting to use it. If the image doesn't exist, it triggers a Docker index refresh.
• Error Handling: Improves error handling by raising a ValueError if the Docker image is not found in the local Docker registry, providing a more informative error message.
• Gitignore Update: Adds the temp/ directory to the .gitignore file, preventing temporary files from being tracked by Git.

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[gemini-code-assist]

Code Review

This pull request aims to improve the Docker image existence check in DockerNotebookSandbox. The proposed change correctly identifies a potential issue with stale Docker indexes but introduces some complexities and anti-patterns. My review focuses on simplifying the logic, making it more robust and idiomatic, and ensuring correct logging behavior. The change to .gitignore is correct and has no issues.