Fix parameter naming from PascalCase to camelCase in ImageCompare.cs

[Copilot]

Addresses code review feedback from #75 regarding C# naming convention violations for method parameters.

Changes

• Renamed Pic1, Pic2 → pic1, pic2 in CalcDiff and CalcDiffMaskImage overloads
• Renamed PathPic1, PathPic2 → pathPic1, pathPic2 in CalcDiffMaskImage
• Renamed PathActual, PathExpected → pathActual, pathExpected in ImagesAreEqual and ImagesHaveEqualSize
• Updated corresponding XML doc <param> tags

// Before
public SKBitmap CalcDiffMaskImage(SKBitmap Pic1, SKBitmap Pic2)

// After
public SKBitmap CalcDiffMaskImage(SKBitmap pic1, SKBitmap pic2)

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