Description

When using surf_source_read from the settings with MCPL files, OpenMC fails and complains about not being able to read it as a HDF5 file. One easy way to avoid this error was to use a openmc.FileSource object and pass it as a settings.source instead.

This PR enables source files in MCPL format to be read when using surf_source_read.

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)