useDiamondMotionSearch property

When true, integer-pel motion search uses a diamond pattern (large + small diamond) instead of the default full-window SAD scan. Trades a small compression cost (typically <2% bytes on VC content with searchRange<=4) for an order-of-magnitude reduction in SAD evaluations at large search ranges. The seed MV (when predictorMotionSearch is on) is still evaluated, so the result is no worse than the trivial predictor pick. Default false keeps the bitstream byte-identical to the baseline full-search encoder.