GeoModelCore/GeoModelIO clang-tidy fixes

GeoModelCore/GeoModelIO clang-tidy fixes

Relates to [#109 (closed)].

These are the ones that can be auto-applied by the tooling so see

/afs/cern.ch/user/c/christos/public/GeoModel_static_check/clang_tidy_log 

for the "reasoning"