Cell (along with other properties) cannot be accessed from `project_hdf5` in Sphinx

[samwaseda]

https://github.com/pyiron/pyiron_atomistics/blob/4361b7b02f89148e249aac04d17dd6eeffdd1bff/pyiron_atomistics/atomistics/job/atomistic.py#L1032

The reason why this line fails is because Sphinx uses DataContainer and has tags like cells__index_2, which obviously is not the same as cells when it's accessed from project_hdf5. I guess this topic really requires an overhaul discussion because it's a recurring issue with no structural solution in the current format