useMvRateCost property

When true, the integer motion search scores each candidate by SAD + ((sadPerBit16 * mvBitCost(mv, defaultMvContext)) >> 8) -- the libvpx Lagrangian rate-distortion formula, where sadPerBit16 is derived from the current base qi via computeRdConsts and mvBitCost is the exact theoretical entropy cost of writing the candidate MV under the default MV probs. When this is true, mvRateBias is ignored by the search.

Default false keeps existing behaviour byte-identical.