Draft: Change AthenaMP chunk size default to dispatch cluster of events for LZMA
This change will have default AthenaMP dispatch chunks of events equal to auto-flush when reading LZMA compressed data (most data PxAOD and up) to avoid duplicating de-compression work. For Run3 this is most applicable for derivation, which will be run in AthenaMP on LZMA data with 100 events per cluster.