Fix record: mago analyze flags loadConstraintDataNames() as unused-method in Metadata/Source.php #63

Context

Part of #60.

Data

mago analyze flags help[unused-method] on Metadata\Source::loadConstraintDataNames(). It writes to $this->data['constraint_names'][$schema], but no other method in Source.php, AbstractSource, or MetadataInterface reads that key or exposes it via a public getter (unlike its sibling loadConstraintDataKeys(), which backs AbstractSource::getConstraintKeys()).

@simon-mundy has the most context on this part of the SQL/metadata handling and knows the scope of the refactor needed here better than we do.

This finding will be captured in a mago baseline rather than fixed or suppressed inline.