Ensure that two surfaces with different boundary type are not considered redundant

[paulromano]

Description

Right now, if you are exporting a model and ask it to remove redundant surfaces (Geometry.merge_surfaces = True), it compares the surface type and coefficients to determine whether two surfaces are considered equivalent. However, the boundary_type is not currently accounted for, which can cause problems if you have one surface with a boundary condition applied and another surface with no BC that is used on a lower universe level. This PR simply makes a change to account for the boundary_type when determining whether two surfaces are equivalent.

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)

[shimwell]

This PR is clear enough that I can review it. All looks good. Thanks for adding the test. I can merge Tuesday afternoon (UK time) if there are no objections