ENH: handle restart files with new ADIOS
- ADIOS-2.4.0 and earlier had timeName.bp files and timeName.bp.dir/ directories. Restart checked for times based on the timeName.bp files - ADIOS-2.5.0 and later simply use timeName/ directories, for which we can use slight modifications of standard OpenFOAM fileOperation routines. Does not handle mixed naming. If the .bp files exist, we assume that they provide full coverage for restart.