[CHORE] Switch to debug_struct over f.write

[HammadB]

Description of changes

Summarize the changes made by this PR.

• Improvements & Bug fixes
  • This switches to debug_struct over f.write as per @rescrv's suggestion.
  • Fixes a spurious warning about an unused struct field
• New functionality
  • None

Test plan

How are these changes tested? We do not test the debug behavior.

• [x] Tests pass locally with pytest for python, yarn test for js, cargo test for rust

Documentation Changes

None

[github-actions[bot]]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

Testing, Bugs, Errors, Logs, Documentation

• [ ] Can you think of any use case in which the code does not behave as intended? Have they been tested?
• [ ] Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• [ ] If appropriate, are there adequate property based tests?
• [ ] If appropriate, are there adequate unit tests?
• [ ] Should any logging, debugging, tracing information be added or removed?
• [ ] Are error messages user-friendly?
• [ ] Have all documentation changes needed been made?
• [ ] Have all non-obvious changes been commented?

  System Compatibility

• [ ] Are there any potential impacts on other parts of the system or backward compatibility?
• [ ] Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

  Quality

• [ ] Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)