🧹 Refactor AverageInt to use integer tuples

[johnstrand]

🎯 What: Replaced individual integer coordinate parameters (ax, ay, etc.) in Diamond.AverageInt with (int x, int y) integer tuples.
💡 Why: Reduces parameter count from 9 down to 5. Unlike System.Numerics.Vector2 which uses floats, (int x, int y) correctly maintains the semantic integer constraints necessary for array/grid indexing without requiring type conversions.
✅ Verification: Verified by running dotnet test tests/GameUtils.Tests. All tests passed.
✨ Result: A cleaner method signature that is less error-prone when passing parameters, maintaining structural integrity with existing indexing operations.

---

PR created automatically by Jules for task 8309767824594684440 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.