test: Validate NumberBox.Value StackOverflow prevention for x:Bind two-way bindings

[Copilot]

GitHub Issue: closes #18619

PR Type:

🧪 Test

What is the current behavior? 🤔

NumberBox.Value setter contains StackOverflow prevention logic for two-way x:Bind scenarios with NaN values, but lacks automated validation. The implementation prevents infinite loops by skipping SetValue when both incoming and current values are NaN (since NaN != NaN).

What is the new behavior? 🚀

Added comprehensive runtime tests validating the StackOverflow prevention:

• NaN→NaN: Verifies SetValue is skipped, preventing infinite loops
• NaN→Number: Validates normal property change behavior
• Number→NaN: Validates clearing values works correctly
• Number→Number: Ensures protection doesn't affect regular updates

Tests confirm Uno Platform's implementation matches WinUI behavior for all x:Bind two-way binding scenarios.

PR Checklist ✅

• 📝 Commits follow Conventional Commits specification
• 🧪 Added Runtime tests for validation
• 📚 Docs not applicable (validation only)
• 🖼️ Screenshots not applicable (test-only PR)
• ❗ Contains NO breaking changes

Other information ℹ️

Implementation already exists in NumberBox.Properties.cs (lines 412-415) and is correct. This PR adds test coverage to prevent regressions.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Validate potential StackOverflow in NumberBox.Value setter</issue_title>
<issue_description>### What would you like to be added

WinUI says the following:

We need to validate this scenario is handled correctly on Uno Platform targets and add test to validate this.

Why is this needed

No response

Renderer

• Skia
• Native

For which platforms

No response

Anything else we need to know?

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Validate potential StackOverflow in NumberBox.Value setter #20458

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