The default key generator: k-sortable UXID strings (ADR-0002 decision 2).
Keys are generated by the uxid package and carry per-table prefixes in
the engine's own style - chart_, pos_, run_ (ADR-0002 decision 4,
as amended) - so a key met in a psql console or a log line names its
table. Stored as :string fields over :text columns.
Options given to the generator (via {module, opts} or the resolved
default) are passed through to UXID.generate!/1; the per-table
:prefix is supplied unless the options already carry one.