🧹 [Code Health] Remove unused import in metrax_test.py

[rni418]

🎯 What: Removed the unused import metrax.nnx from src/metrax/metrax_test.py.
💡 Why: The import was not being used anywhere in the file. Removing it cleans up the codebase and improves code readability and maintainability.
✅ Verification: Verified that the removal didn't cause any test failures by running the full unit test suite python3 -m unittest src/metrax/metrax_test.py.
✨ Result: Improved code health in src/metrax/metrax_test.py by eliminating dead code (the unused import) without breaking functionality.

---

PR created automatically by Jules for task 11119655779190449620 started by @rni418

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.