Keep centered text ink within finite view bounds

[Happypig375]

Summary

• add an explicit finite-region TextPainter.Draw overload that preserves the region origin while applying caller offsets
• constrain Uno text layout to the control's content width and route the Uno text view through the finite-region path
• compute positioned ink bounds for centered text and clamp only overflowing centered ink, while leaving the legacy drawing geometry unchanged
• cover finite-width wrapping, non-zero origins/offsets, centered overhangs, and the legacy/unbounded contract

Validation

• CSharpMath.Rendering.Tests.TestTextBounds: 12/12 passed
• full CSharpMath.Rendering.Tests: 1,238/1,238 passed
• CSharpMath.Xaml.Uno Release build passed
• Public API checks passed for Debug and Release
• scoped formatting verification and git diff --check passed

The production Uno path compiles and is covered below the control boundary. A hosted Uno runtime-control test would require the app-host setup described in Uno's runtime testing documentation, which this repository does not currently contain.

Fixes #174