fix expansion filter merging

[gridley]

Description

Lets expansion filters be merged by addressing the fact that they don't just take a list of bins as a constructor argument.

Fixes #2881

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 @gridley!