Co-authored-by: Andre Sailer <andre.philippe.sailer@cern.ch>

Co-authored-by: Andre Sailer <andre.philippe.sailer@cern.ch>

Remove support for very old versions of ROOT < 6.26.0. Remove default use of std namespace from some implementation files.

Geant4InputHandling: prevent adding same particle more than once

Geant4InputHandling: collectPrimaries: use the mask to place the daughter vertices rather than size of the map

Now every place where interaction->vertices map is being used, the mask is used as the key to the map, instead of something else

`imp` was removed in Python 3.12.

Since 1.26 (ab9a96e6) we are seeing `ddsim` exceptions on certain Open Science Grid nodes/sites. Those sites appear to configure the running of singularity containers in such a way that no usernames are associated with the uid.

This is done by actually reading an event instead of skipping one.
Skipping may be sufficient for the ASCII reader, however, RootTree reader does not perform a read on skip:
https://gitlab.cern.ch/hepmc/HepMC3/-/blob/master/rootIO/src/ReaderRootTree.cc#L76-80