Rename compartmentalmodel to compartmental_model

### Motivation / Current Behaviour

`cpp/memilio/compartments/compartmentalmodel.h` should be named according to the convention to `cpp/memilio/compartments/compartmental_model.h`

This will also affect some includes.

### Enhancement description

see title

### Additional context

_No response_

### Checklist

- [x] Attached labels, especially loc:: or model:: labels.
- [x] Linked to project