RootStorageSvc+DerivationFrameworkTrainsART: Improve testing for index_ref collisions in derivation jobs (see !50140)
This MR adds a new script to RootStorageSvc (primarily because this is where the index_ref code resides), that given a ROOT file simply loops over all the events and checks for possible collisions in the index_ref values. This is to catch issues that are discussed in !50140 (merged). The new script is also adopted in the ART tests that run as part of DerivationFrameworkTrainsART. So, if this one gets merged before !50140 (merged) (or whatever MR that fixes the underlying issue) then the relevant ART tests should start failing, meaning they're doing their job.