tryGoldenZeroMv property

When true, each inter MB additionally evaluates ZEROMV against the GOLDEN reference and may pick it over the refLast-based best candidate. Lets MBs whose LAST-relative SAD has drifted (an occlusion just ended, a packet-loss artifact still lives in LAST, etc.) fall back to the cleaner long-term reference. Only the ZEROMV mode is considered against GOLDEN — no MV bits are spent, just the extra ref-frame bit. Pairs with goldenRefreshPeriod. Default false keeps existing behaviour byte-identical.