Carry backed-vs-unbacked by permit identity across GraphitronType and ReturnTypeRef

JooqTableRecordType is minted with a null fqClassName at three main-source sites (FieldBuilder twice, TypeBuilder once) as a stand-in for "the parent’s runtime source is a projected table row"; nothing is reflected there, so the class slot is meaningless for that population. A distinct class-less JooqRecordCarrier arm (e.g. TableRowType(name, location, table)) makes fqClassName() non-null across every remaining arm with no requireNonNull needed.

PojoInputType carries backing as a nullable class where PojoResultType split into permits; CatalogBuilder.projectTypeBackingShapes forks it on fqClassName() == null into a result-named NoBacking.UnbackedResult() carrier for an input type. Split into Backed/Unbacked mirroring the result side so the projection seam is an exhaustive switch, not a null check.

ReturnTypeRef.ResultReturnType#fqClassName is the same fact copied into a second record with the opposite nullability contract ("taken directly from the corresponding GraphitronType.ResultType …​ May be null`"), with four `FieldBuilder consumers forking on the null; a derived fact maintained apart from its source. Carry the resolved ResultType (or its arm identity) instead of a re-copied string so the forks become sealed switches.