Specifies file saving modes for IG_mpi_file_save function.
Values:
| IG_MPI_SAVE_OVERWRITE | Replace all existing pages with new ones. |
| IG_MPI_SAVE_APPEND | Append new pages at the end of file. |
| IG_MPI_SAVE_INSERT | Insert pages into the file at the specified index. |
| IG_MPI_SAVE_REPLACE | Replace pages starting from the specified page index. |