Add automatic TSLength calculation and tsIndex to TimesliceMetaData (mcbm2020 unpacking)

Up to now the TS length was hardcoded for the TimesliceMetaData object. This commit adds an automatic calculation and inserts it into the stored TimesliceMetaData objects.

assigned to @p.-a.loizeau

approved this merge request

@p.-a.loizeau could you have look, since, it changes the unpacking source class.

enabled an automatic merge when the pipeline for c5d56bc1 succeeds

merged