[ENHANCEMENT] Investigate removing IOutputVariable and subclasses

[oerc0122]

Is your feature request related to a problem? Please describe. The MDANSE.Framework.OutputVariables.IOutputVariable and subclasses (LineOutputVariable, SurfaceOutputVariable and VolumeOutputVariable) and associated OutputData object seem to be vestigial objects.

Describe the solution you'd like It may be possible to either remove them entirely or replace them with standard xarray data. xarray integrates seamlessly with dask (see #443), h5py, matplotlib and pint and provides the metadata features which IOutputVariable attempts to include.

Describe alternatives you've considered N/A

Additional context N/A