API: rethink duplicated namespaces e.g. in solarsystem

Recently we run into the issue of #3100 where warnings were issues due to classes being exposed in multiple namespaces.

The issue is not worked around with a version pin, so building the docs keep working, but we may need to rethink our approach.

Start by reading issue #3100 and examining how the solarsystem resource exposes classes in multiple namespaces. Check the documentation build warnings and identify the affected namespace definitions; done requires an agreed approach for avoiding duplicated exposure without relying on a version pin.

Written by the indexing model from the issue text.