Clunky examples of new-style settings object use in docs

The relevant documentation is here: https://fluent.docs.pyansys.com/version/stable/user_guide/solver_settings/solver_settings_contents.html.

Adjusting the imports will make it look neater:

```Python
from ansys.fluent.core.solver import VelocityInlet, Viscous  

inlet1 = VelocityInlet(settings_source=solver, name="inlet-1")  
viscous = Viscous(settings_source=solver)  
viscous.model()
```