Fix Magick.NET v14 breaking API changes in UITest.cs

[Copilot]

After bumping Magick.NET-Q8-AnyCPU from 13.5.0 to 14.10.2, UITest.cs failed to compile due to two v14 breaking changes not addressed by the initial fix.

Changes

• ImageMagick.Drawing namespace: Drawables and all drawing classes moved out of ImageMagick into ImageMagick.Drawing in v14. Added the missing using ImageMagick.Drawing;.
• MagickImage constructor: (IMagickColor, uint width, uint height) — width/height params changed from int to uint. Added (uint) casts on the int values sourced from GetRect().

// Before (v13)
using var surface = new MagickImage(MagickColors.Transparent, width, height);
new Drawables()  // CS0246: type not found — Drawables moved to ImageMagick.Drawing

// After (v14)
using ImageMagick.Drawing;
// ...
using var surface = new MagickImage(MagickColors.Transparent, (uint)width, (uint)height);
new Drawables()  // resolves correctly

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