Fix compatibility with Pydantic 2.13

[mattwthompson]

Description

Possible fix for #1346

Checklist

• Add tests
• Lint
• Update docstrings

[mattwthompson]

De-serialization of collections is failing by not picking up non-default values. The fix is probably straightforward but I don't have more time to work on this today

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.07%. Comparing base (90e49b8) to head (dfeb1a4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1501   +/-   ##
=======================================
  Coverage   94.07%   94.07%           
=======================================
  Files          73       73           
  Lines        6055     6058    +3     
=======================================
+ Hits         5696     5699    +3     
  Misses        359      359           

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[mattwthompson]

Failure is at a serialization time, not de-serialization

In [32]: state1.collections['Electrostatics'].scale_14
Out[32]: 0.8333333333

In [33]: with open("test.json", "w") as f:
    ...:     f.write(state1.model_dump_json())
    ...:

In [34]: json.loads(open('test.json').read())['collections']['Electrostatics'].keys()
Out[34]: dict_keys(['type', 'is_plugin', 'expression', 'key_map', 'potentials'])

In [35]: json.loads(open('test.json').read())['collections']['Electrostatics']['scale_14']
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[35], line 1
----> 1 json.loads(open('test.json').read())['collections']['Electrostatics']['scale_14']

KeyError: 'scale_14'