Draft: Fix helium HLT2 lines
Switch the particle combiner from DecayTreeFitter to `OfflineVertexFitter and re-include helium lines.
This is intended to be a fix for #827 (closed).
Relies on LHCb!4662
Switch the particle combiner from DecayTreeFitter to `OfflineVertexFitter and re-include helium lines.
This is intended to be a fix for #827 (closed).
Relies on LHCb!4662