🧪 test: Add unit tests for Polygon2D translation and construction

[johnstrand]

🧪 [testing improvement description] Add unit tests for Polygon2D.TranslateBy and Polygon2D constructor.

🎯 What: Added tests for the previously untested Polygon2D.TranslateBy method and constructor validation in Polygon2D.
📊 Coverage: Covered single vector translation, zero vector translation, multiple cumulative translations, vertex/edge/bounding box state verification after translation, and empty vertices exception handling.
✨ Result: Improved test coverage and reliability for Polygon2D.

---

PR created automatically by Jules for task 5593915913291489980 started by @johnstrand

[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.