Dispose ONLY the custom-LUT colormap texture cache.
Custom LUTs are scene/dataset-scoped. SceneLoader.dispose() reaches
this on dataset unload (through releaseCustomColormapTextures,
once no other live dataset holds the cache) so unused custom textures
don't accumulate across many dataset switches in a long-lived app.
Built-ins are not touched.
Dispose ONLY the custom-LUT colormap texture cache.
Custom LUTs are scene/dataset-scoped. SceneLoader.dispose() reaches this on dataset unload (through releaseCustomColormapTextures, once no other live dataset holds the cache) so unused custom textures don't accumulate across many dataset switches in a long-lived app. Built-ins are not touched.