Available as MMCifEntityDesc objects in MMCifInfo

If all residues in a chain are saccharides in some form, the
respective _entity.type should be "branched"

Minimum length for a chain in the target structure
to be considered in chain mapping. The chain mapping algorithm first
performs an all vs. all pairwise sequence alignment to identify
"equal" chains within the target structure. We go for simple sequence
identity there. Short sequences can be problematic as they may
produce high sequence identity alignments by pure chance.

BUT: if you're scoring peptides or short nucleotides, you
really want to be able to reduce the default thresholds
(pep: 10, nuc: 4)

Right now there is only a static constructor for polymer entities

uint8_t got interpreted as char, it's integer now

Some ligands like YUT (in CAMEO 2023-12-30_00000023/8G9C) have a huge
number of isomorphic mappings and cause CAMEO to run out of time in the
scoring (and fail horribly). This allows to limit how much time is spent
listing all the isomorphisms. 100000 (1e5) seems reasonable and ensures
the scoring completes in minutes. Computing RMSD with SCRMSD is a bit
faster and 1000000 (1e6) should be OK.

New unassignment reasons are introduced as well.