Bugfix: Retrieve correct time steps when time is across file dimension and the time steps of the first files are skipped

Correct dat name of work_pieces (internal usage only); Add message when multiple datasets are requested and return_vars has common dimensions

Change autosubmit 'THREADS' back  to 'cores_per_job'; Modify documentation about ncores and num_procs

Fix metadata reshaping when time dim is implicit and the split file dim array has time as a dimension