StatsWidget: multiple widgets incorrectly merged into single list

[ibgreen]

Repros in https://loaders.gl/examples/3d-tiles

[isaacbrodsky]

I think this may have been fixed in #166

[ibgreen]

@dryabinin-actionengine @belom88 Maybe you can try probe.gl v3.5.0-alpha.3 in loaders.gl examples to see if this is fixed?