We should disallow importing modules with virtual streams that overlap with real streams of the same module. This is because in _add_base_module_provides, there is code that adds provides for the base module's stream and all of its virtual streams. If this base module provided a virtual stream that overlaps with a real module's stream, libsolv could potentially pick the wrong base module.

We haven't run into this in production, but this is just a precaution since in practice, a non-MBS maintainer can import modules.