tolerancePercent

Share of pixels allowed to differ before a comparison fails. Unset by default, leaving viddik's own 0.05% (plus a ±2 per-channel allowance), which is what the residual cross-OS difference measures once fixtures bundle a font. Becomes the viddik.tolerancePercent system property.

This is the threshold for the whole module. A single fixture that provably can't hold it says so itself — @ViddikScreenshot(tolerancePercent = ...) — rather than being paid for by loosening the check on every other fixture.