Move sofar-related pyfar functionality to sofar

In https://github.com/pyfar/pyfar/issues/958, we decided to

• move the functionality pyfar.io.read_sofa and convert_sofa to sofar
• implement possibly identical behavior to the classes Sofa and SofaStream
• improve flexibility to return arbitrary coordinates

I would suggest to add methods as_audio_object and as_coordinates.

as_audio_object()

• will return values in Sofa.Data as a pyfar Signal or FrequencyData depnding on the data type of the Sofa object
• In case of SofaStream it could have an addition parameter slice to determine which data is returned

as_coordinates(attribute)

• works as the above, with attribute determining which data of the Sofa object is returned as coordinates
• also has the additional slice parameter for SofaStream

The only difference between Sofa and SofaStream methods is how the actual data is obtained. Everything else can be moved into shared private functions to avoid redundant code.

If we consider this to be some kind of I/O functionality, it might be more consistent to implement this as sofar.as_audio_object otherwise it could be Sofa.as_audio_object and SofaStream.as_audio_object.