LoadBalance of GeometryGrid is deactivated

When using a GeometryGrid wrapper in parallel, it is surprising that the loadBalance(...) functions are actually commented out. The effect is that the GridDefaultImplementation is used, which means: no load balancing at all. This means, GeometryGrid cannot be used with most grid managers that require a loadBalance() call after setup (except if you call that function on the host grid directly).

The corresponding code, see https://gitlab.dune-project.org/core/dune-grid/-/blob/master/dune/grid/geometrygrid/grid.hh?ref_type=heads#L437 simply has an #if 0 without proper documentation why, since about 13y. So, no-one used GeometryGrid in parallel since then?

In my opinion, the behavior is a bug. The proper behavior would be at least an error message if that function does not work with the GeometryGrid wrapper. One aspect could probably be difficult: If a DiscreteCoordFunction is used that is based on discrete data, then this data also needs to be communicated in the load-balancing step. But, I think, this could be implemented.