OptionalMetadataOptional structured metadata. Useful when callers want to attach filterable/sortable attributes to a registration without polluting the Key string (e.g. form-panel slots: { entity, slot, sortKey }).
Pair with ClassFactory.GetAllRegistrationsByMetadata() /
GetAllRegistrationsByKeyPrefix() / GetAllRegistrationsByKeyPattern()
to discover registrations beyond exact-key matching.
Data structure to track the class registrations