Renames RifSummaryReaderMultipleFiles to RifSummaryReaderAggregator
to better reflect its purpose of aggregating summary data from multiple files. Also avoid confusion with RifMultipleSummaryReaders
Testing identified performance issues related to reading restart file name from summary files.
Make sure the reading of timesteps is done only when required in new function getFileInfoAndTimeSteps.
Add reading of restart file name using opm-common when opm-common is active. The performance of this reader is much better than resdata.