utilities list_h5_files relies on time step in file name

[PrometheusPi]

Currently, all time series extractions are done using the list_h5_files function from opmd_viewer.openpmd_timeseries.main. This function extracts the time step from the last number before the suffix not from the time step in the hdf5 files. See code here. Thus files like libSplash serial output will result in wrong time steps (the serial output extracts files with a given mpi rank as filename_[timestep]_[rankx]_[ranky]_[rankz].h5).

[RemiLehe]

Thanks for pointing out this issue!
Would you have the time to do a pull request to correct this? Otherwise I can also do it.

[PrometheusPi]

No problem. I will provide a pull request.