Optimize Geant4VolumeManager

[MarkusFrankATcernch]

BEGINRELEASENOTES

• Optimize the Geant4VolumeManager. Instead of mapping the Geant4 pathes as vectors of pointers,
  hash64 the pointers of the path and lookup pathes from the touchable history using this key.
• Relevant changes are in the files DDG4/Geant4GeometryInfo.h and src/Geant4VolumeManager.cpp.
  Everything else is only cosmetics.

ENDRELEASENOTES

[github-actions]

Test Results

   16 files     16 suites   6h 7m 29s ⏱️
  370 tests   370 ✅ 0 💤 0 ❌
2 887 runs  2 887 ✅ 0 💤 0 ❌

Results for commit 3984eec.

♻️ This comment has been updated with latest results.

[MarkusFrankATcernch]

This MR should optimize the memory usage of the Geany4VolumeManager in
up to some degree should overcome the need to use #1288.
The memory consumption of the Geany4VolumeManager as presented here should be largely reduced: instead of performing lookups with vectors of pointers as key only 64bit hash values are used.