Fix 313 enum variants

[JR-1991]

As highlighted in #72 the enumeration variants for units need to explicitly implement enum.members to allow the usage of partial in a non-context environment. Tests have been extended to Python 3.13 to check possible other future incompatibilites.

@jmrohwer can you please test it to verify it is working on your machine too?

• Closes importing pyenzyme fails under Python 3.13 (v2-migration branch) #72

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[jmrohwer]

👍 Works for me as well

[JR-1991]

@jmrohwer perfect, thanks! Merged 🙌