Fix parameter naming conventions in ImageCompare.cs

[Copilot]

Addresses code review feedback from #75 about inconsistent parameter naming. Parameters were using PascalCase instead of C# convention camelCase.

Changes

• CalcDiff: Pic1, Pic2 → pic1, pic2
• CalcDiffMaskImage (string): PathPic1, PathPic2 → pathPic1, pathPic2
• CalcDiffMaskImage (SKBitmap): Pic1, Pic2 → pic1, pic2
• ImagesAreEqual: PathActual, PathExpected → pathActual, pathExpected
• ImagesHaveEqualSize: PathActual, PathExpected → pathActual, pathExpected

All XML doc comments and method body references updated accordingly.

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