Fix parameter naming to use camelCase in ImageCompare.cs

[Copilot]

Addresses code review feedback from #75 regarding inconsistent parameter naming. Several method parameters used PascalCase instead of C# convention camelCase.

Changes

• CalcDiff(SKBitmap, SKBitmap, SKBitmap): Pic1, Pic2 → pic1, pic2
• CalcDiffMaskImage(string, string): PathPic1, PathPic2 → pathPic1, pathPic2
• CalcDiffMaskImage(SKBitmap, SKBitmap): Pic1, Pic2 → pic1, pic2

Updated both parameter declarations and corresponding XML doc <param> tags.

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