[ENHANCEMENT] Investigate removing IOutputVariable and subclasses

**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`](https://docs.xarray.dev/en/stable/) data. `xarray` integrates seamlessly with `dask` (see #443), `h5py`, `matplotlib` and [`pint`](https://pint.readthedocs.io/en/stable/) and provides the metadata features which `IOutputVariable` attempts to include.

**Describe alternatives you've considered**
N/A

**Additional context**
N/A