This is the last piece (on the infrastructure part) needed to correctly use CALO with both DD4hep & DetDesc. Together with !957 (merged) it will correctly generate G4hits, extract them to MCCaloHits and produce histograms.
The only thing missing is the dd4hep cellID lookup that @dmanuzzi started working on in !953. In any case, the dd4hep implementation here will run without throwing errors (it will create empty hits), so that we can already include Calo in the LHCbPR tests and test the results of !953 later.
@dmanuzzi as you can see I am targeting your branch, i.e.
dmanuzzi_CALO_DD4HEP_v3, because otherwise this MR would create conflicts. We can include it in the tests once you solve the threads and we merge !950 (merged) to Futurev5.