axis unit setting via ax.units = val setter does not update attrs for the parent object

[ksunden]

This results in the units not being updated on disk despite working in memory for the new units

should either be reworked to call the update parent attrs function that is called in convert or to just call convert (and thus have convert set self._units to avoid infinite recursion)

Which option depends on if we wish to allow you to set units via units setter to units that would otherwise raise an exception in convert.