A pre-validated handle to a UObject. Proves that the object was alive
at the time of validation. Used as the receiver for codegen extension
trait methods, which can then skip per-call validity checks.
A typed reference the engine passes as a UObject*: an object
(UObjectRef<T>) or a class (SubclassOf<T>, a UClass*). The generated
bindings convert through it, so the declared type decides which one.