Add C API function for getting mesh bins for rasterized plot

[paulromano]

Description

This PR adds a new openmc_mesh_get_plot_bins function and corresponding openmc.lib.Mesh.get_plot_bins Python binding that allows you to determine the mesh bin indices for pixels on a 2D rasterized plot. I'm planning on integrating this into openmc-plotter to generalize our mesh plotting capabilities there. For example, here is a sneak peak of a tet mesh tally visualized in the plotter:

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)

[paulromano]

FYI It looks like there were a bunch of CI test failures related to a new release of scipy. I've limited the range of valid scipy versions to <1.12 to avoid this for now while I look into what's going on with the new version.

[pshriwise]

Awesome PR @paulromano! I'll keep an eye on CI. Once that passes, I don't see a reason not to get this merged in soon. 🕵🏻

[shimwell]

Do we have to update the conda meta.yml to also have this scipy restriction

[paulromano]

@shimwell I'm going to look into what is going wrong with scipy 1.12 and get it fixed before the next release, so we shouldn't need to worry about conda.