CalorimeterTruthCluster may need an update

[ruse-traveler]

After looking at CalorimeterTruthCluster recently, it appears to be significantly out-of-date.

Namely:

1. Sim and rec hits are assumed to be 1-to-1, which is not necessarily true and could be better handled by utilizing sim-rec hit associations; and
2. Rec hits are sorted by the MC particle associated with the first (in entry order) contribution to the hit, which is at odds with how we assign MC particle-cluster associations.

While item 1 is a straightforward fix, I want to check my understanding on item 2:

• The algorithm's description states that it uses truth information for clustering,
• So I would expect the algorithm to group rec hits according to the MC particles that "caused" them,
• But that's ambiguous since there's always the possibility that multiple particles contributed to a rec hit,
• And so the tactic used here is to select the particle that caused the first contribution.

Would it make sense here to take a similar tactic to the MC-cluster associations and sort rec hits based on the particle that contributed the most energy?