Documentation TOC is based on internal/invisible structures

### Description of the modifications

This package uses various internal groupings, such as putting all the scalar value implementations into `scalar_values.py`. However, this is just internal grouping and has no meaning externally. Externally you would merely use the main package:

```Python
from ansys.tools.variableinterop import RealValue
```

The TOC on the documentation page is split up based on the internal groupings, not based on the external view of the package. This makes it difficult to find what you are looking for (I in fact thought that RealValue was not documented at all for a minute).

RealValue is hidden inside this TOC entry:

### Useful links and references

_No response_

Start by examining how the documentation TOC represents the contents of scalar_values.py and other internal groupings. Compare those entries with the public import from ansys.tools.variableinterop, including RealValue. Done means the TOC reflects the externally usable package structure and makes RealValue easy to find.

Written by the indexing model from the issue text.