Enforce lower_left in lattice geometry

[kmeag]

Description

When exporting a lattice geometry to XML without the lower_left specified, an error is thrown that is hard to debug. I localized this in the code and threw a helpful error so that a user is less frustrated when this happens.

ValueError: Lattice 1 <lower_left> has not been specified.

Fixes #2902

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]

Thanks @kmeag!