Move generator status setting to common place

GenerationActionInit: declare properties to access number of processed runs and events

We no longer test with ROOT 6.22, and in 6.32 PyROOT is coming back but subtly fails on macOS

Avoid having another level of quotes or b'' showing up in the wrong places

Typename: do not inherit from std::pair because ROOT stopped working for this construct for some reason

when the value is used as 'half-length'
replacing GetNegativeEndZ by GetPositiveEndZ fixes the problem
because GetPositiveEndZ is the user value that corresponds to half-length

LCIO now exports LCIO::lcio, so we could use that if LCIO is new enough

Explicity set namespace to TrackClassification in
TestStackingAction::classifyNewTrack