Implement the i/o changes to handle the zoom case

Features:

• Indicate in the header whether this is a Zoom or not.
• Undo the zoom region shift when writing particles. Only in multi-soft gpart and SPHENIX hydro for now.
• The shift is also removed from the top-level cell meta-data.
• The Origin is added to the cell meta-data.
• The cell meta-data only uses the zoom region information.
• The header reports NumParticles_OutsideCells and NumParticles_InCells

See https://github.com/SWIFTSIM/swiftsimio/issues/188.

Todo:

• Same for the other particle i/o cases.
• Add NumParticles_InCells and NumParticles_OutsideCells also in MPI case.