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

I hope this will work fine. If the list of headers or linkdefs changes, then cmake should re-run anyway and that will call the file(Generate) to recreate the script, and if only the file content of headers or linkdefs changes, we only have to re-run the shell script.