Allow OpenMC to compile against fmt v9

[andrsd]

This fixes the build of OpenMC against fmt v9.x.

[andrsd]

Without this patch, the build fails with:

openmc/src/geometry.cpp:314:12: note: in instantiation of function template specialization 'fmt::format<int &, int &, int &, int &, openmc::Position &>' requested here
      fmt::format("    Crossing lattice {}. Current position ({},{},{}). r={}",

and also on:

openmc/src/output.cpp:196:10: note: in instantiation of function template specialization 'fmt::print<openmc::Position &>' requested here
    fmt::print("    r = {}\n", p.coord(i).r);

on develop branch.

The position structure is printed as (x, y, z). IDK if that's the format you would prefer, but can be easily changed.

I triggered this problem when cmake picked up my fmt library installed via conda on a MacOS.

Let me know if you need any additional information.

[paulromano]

Thanks for the fix @andrsd! We use clang-format for our C++ code (there's a .clang-format file in the root of the repo). To make things easy, I've given a suggested change here with the results of applying clang-format. Once that's updated, I'll trigger CI and assuming all is good we can merge.

[andrsd]

Thanks for merging and your help with getting this into upstream!

[paulromano]

Absolutely, and thank you for helping to improve the code!