Muon BS to RDO caching for multi-threading - CSC technology

This MR (WIP for now) continues the work initiated by @markowen, and was closed during the private->public repository migration (see athenaprivate1!16700). As this was a branch off of Mark's fork, it was not straight-forward to patch so I have had to do a manual diff/merge procedure to bring into the new repository. The code is currently compiling correctly but will need to be tested as it is further developed.