Resolves Adjustment 4 (Option A): WorldEntity now carries the server-
sent AnimPartChange data as PartOverrides and a HiddenPartsMask bitmask.
EntitySpawnAdapter.OnCreate populates AnimatedEntityState from these
fields at spawn time. GameWindow's CreateObject handler converts the
network-layer AnimPartChange records into lightweight PartOverride
structs.
This unblocks Task 22: the WbDrawDispatcher can now resolve per-part
GfxObj overrides and hidden-part suppression from entity state.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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