Fix pickling error that occurs with scipy>=1.18

[c-randall]

Description

As of scipy 1.18, some objects carry references to numpy and/or other modules. This creates an issue when creating deep copies or pickling. This update fixes this issue by ensuring the deepcopy method doesn't try to pickle modules. Instead, when objects are copied that store modules, the copy just returns the same reference to the stored module, since modules act as singletons.

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that improves speed/readability/etc.)
• Bug fix (non-breaking change which fixes an issue)
• Chore (any other clean up, maintenance, etc.)

Key checklist:

• No style issues: $ nox -s linter [-- format]
• Code is free of misspellings: $ nox -s codespell [-- write]
• All tests pass: $ nox -s tests

Further checks:

• The documentation builds: $ nox -s docs.
• Code is commented, particularly in hard-to-understand areas.
• Tests are added that prove fix is effective or that feature works.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.46%. Comparing base (4905761) to head (ee8547c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #28      +/-   ##
==========================================
+ Coverage   91.45%   91.46%   +0.01%     
==========================================
  Files          31       31              
  Lines        2234     2238       +4     
==========================================
+ Hits         2043     2047       +4     
  Misses        191      191              

Flag	Coverage Δ
unittests	91.46% <100.00%> (+0.01%)	⬆️

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