Enumeration range for cell lengths about cif_core HOT 2 CLOSED

@nautolycus this was indeed previously somewhat discussed in issue #64. The conclusion for the _cell_length_* items was to choose 1.0: as the new enumeration range based on the radius of a hydrogen atom and to backport this change to the legacy version of the DDL1 CIF_CORE dictionary (see https://github.com/COMCIFS/DDL1-legacy-dictionaries/blob/main/dictionaries/cif_core.dic where is change is already present since around 2017).

However, I think that the enumeration range can be changed (back) to 0.0: in both the DDL1 and the DDLm versions if needed without having a significant effect on the validation of existing CIF files. Personally, I also like the 0.0: enumeration range better, but maybe @jamesrhester knowns the original reasoning that led to this change when migrating from DDL1 to DDLm?

from cif_core.

I have no insight to offer here, beyond supposing that perhaps certain dREL methods may have failed if provided with a zero-valued cell length, and so a minimal sensible value was chosen. I'm pretty certain there was no public discussion of this change, so reverting it would not be a problem. I have no objection to going back to 0.0.

from cif_core.