AthenaConfiguration+AthenaMP+AthenaPool+PyJobTransforms: Disable Parallel Compression (while using SharedWriter) if there are not enough events to process
As discussed in ATLASJT-428, running AthenaMP+SharedWriter jobs w/ too few events where one uses parallel compression can be problematic. Now, if we don't have "enough" events, we automatically disable this feature and fallback to the legacy SharedWriter. Any cross-check/feedback is most welcome...