[Custom Issue]: Add dummy functions for MPI IO operations

[t00sa]

Contact Details

No response

Are there any linked Issues or Pull Requests?

Yes! PR #197

Brief description

A bit of outstanding technical debt from identified by Andrew Coughtrie (@andrewcoughtrie) as part of his review of the PR:

My thoughts are both that this shouldn't be kept in the mpi_context.cpp file it would probably be preferable to wrap/dummy the actual MPI calls and have the actually use in the single.cpp file. This would keep the MPI usage contained away from our usage in the writers.

Further details of the issue.

A big chunk of code in mpi_context.cpp is currently ifdefed out when MPI isn't available. This should be replaced with some dummy functions to make it consistent with the approach used elsewhere in the code base.

[andrewcoughtrie]

Since Maff Glover (@mo-mglover) said he wanted to look at this I've assigned the issue to him.