AnalysisBase EL9 Fixes, main branch (2023.10.19.)

Gave an explicit constructor and destructor to JetPileupTag::JetVertexNNTagger, fixing ATLASG-2619.

This one was kind of interesting. 🤔 I could find pretty quickly that the issue was with this tool, that just required some GDB play-time. (The crash backtrace was very clear that ROOT couldn't construct one of the analysis algorithms/tools.) I even concluded fairly quickly that it was the lwtnn member variable that was causing the issue. But I spent quite some time trying to come up with the best solution to the problem.

In the end this is what I came up with. By implementing an explicit constructor and destructor for the class, which are both "implemented" in its source file, ROOT no longer needs to worry about how to actually create or destroy the object. It can just rely on the code that the standard C++ compiler made. This seemed much better than trying to teach Cling how to handle lwt::generic::FastGraph<double> correctly. 🤔

While at it, I also added a small fix for the one compilation warning that we have in the nightly. 😉