Filesystem: Consider mpifileutils?

We currently ship our own set of filesystem functions to create / handle dirs and files on the OS we support.

Much of it could be simplified with C++ filesystem support, which is still not production ready in tooling and broad support.

On top of that, for MPI-parallel operations such as an `mkdir -p` for a series, we do implement safe but potentially meta-data-server "heavy" operations. We could explore if functionality from [mpifileutils](https://github.com/hpc/mpifileutils) can be included/used if this becomes problematic at some point.