fix: offer the whole inheritance chain of a copied class (GH-259)

[spah-soptim]

Summary

CopyClassReferenceResolver walked each copied class exactly once, so it only ever saw the direct super class. Copying GeneratingUnit out of an SSH schema therefore listed Equipment alone, while PowerSystemResource and IdentifiedObject above it were never discovered - not even the client could ask for them, because CopyClassService filters the resolver's output by URI, so a class the resolver never returned cannot be selected. Only data types were resolved transitively, because they are copied with their attributes.

The pasted Equipment stub then lost its own super class as well: resolvableSuperClass dropped the link whenever the grandparent was neither copied nor already in the target, which severed the hierarchy instead of truncating it - and contradicted the top-level class, which keeps a left-behind super class as a reference.

• resolve() now follows inheritance up to the root, naming every ancestor after the sub class that inherits from it, so the dialog reads "Equipment -> PowerSystemResource"
• the walk stops above a class the target graph already defines: that class is not copied, so its super class would land in the target with nothing inheriting from it
• a round that discovers nothing new ends the walk, which also terminates a cyclic hierarchy
• a copied stub keeps its super class like the pasted class does, dangling as a reference when the ancestor stays behind, and drops it when the paste asks for no inheritance
• the target graph is read only when there is a chain to walk at all

Related Issues

Closes #259

Checklist

• Tests added or updated (or not applicable)
• Documentation updated (or not applicable)
• No breaking changes introduced (or described in the summary above)
• Commits are signed off (git commit -s) for DCO

Testing Notes