ReaderPlugin loaded HepMC3::Reader subclasses don't expose their run_info correctly

Because the ReaderPlugin Reader subclass composites the concrete Reader as a data member, calling Reader::run_info on a reader instantiated via deduce_reader never obtains the GenRunInfo read from a file.

It is possible that the intended way to retrieve the relevant GenRunInfo is always from the shared_ptr on a GenEvent instance, in which case this does work, but calling ReaderPlugin::run_info always returns a nulled std::shared_ptr<GenRunInfo> instance.