gameObjectDisplayIdWmoCache_ was not cleared on world unload/transition,
causing stale WMO model IDs (e.g. 40006, 40003) to be looked up after
the renderer cleared its model list, resulting in "Cannot create instance
of unloaded WMO model" errors on zone re-entry.
Changes:
- Clear gameObjectDisplayIdWmoCache_ alongside other GO caches on world reset
- Add WMORenderer::isModelLoaded() for cache-hit validation
- Inline GO WMO path now verifies cached model is still renderer-resident
before using it; evicts stale entries and falls back to reload
85767187b1