Census folds entity-qualified namespaces for some registries but not others

[realmarcin]

From the round-2 review of #244 (#84).

The census folds entity-qualified namespaces into their registry for some registries:

• gold.ecosystem, bacdive.isolation_source and pubchem.compound, before Fold every spelling of a registry the census already counts #244;
• kegg.compound, kegg.drug, KEGG_REACTION, img.taxon, mediadive.* and pubchem.aid, in Fold every spelling of a registry the census already counts #244.

The same shape stays unfolded for other counted heatmap registries:

namespace	registry	Mech	occurrences
gtdb.genome	GTDB	TaxonMech	135,164
pdb.ligand	PDB	ProteinTraitsMech	14,863
pdb-ccd	PDB	AntibioticMech	333
uniprot.location	UniProt	CellStructureMech	656
uniprot.ptm	UniProt	ProteinTraitsMech	468
UniProtKB-KW	UniProt	ProteinTraitsMech	127
RHEA-COMP	RHEA	ProteinTraitsMech	11,169, in grounding: fields

TaxonMech's genome_id: field holds both img.taxon: (counted) and gtdb.genome: (dropped). The README's stated rule doesn't match the code.

Fix: write down one rule and apply it evenly. The precedent in norm is to fold every namespace named for or qualified by a counted registry into that registry.