Add option to determine waste disposal rating by nuclide

[paulromano]

Description

This is a quick follow-up to #3366 that introduces a by_nuclide argument on Material.waste_disposal_rating so that a user can inspect which nuclides contribute most to the waste disposal rating.

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)

[gonuke]

This looks good to me.