Started testing against python 3.15 dev releases.

[MicahGale]

Pull Request Checklist for MontePy

Description

Quick PR to start testing against Python 3.15-dev so we are ready for the release in October.

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General Checklist

• I have performed a self-review of my own code.
• The code follows the standards outlined in the development documentation.
• I have formatted my code with black version 25 or 26.
• I have added tests that prove my fix is effective or that my feature works (if applicable).

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LLM Disclosure

1. Are you?

   • A human user
   • A large language model (LLM), including ones acting on behalf of a human

2. Were any large language models (LLM or "AI") used in to generate any of this code?

• Yes
  • Model(s) used: Claude (sonnet 4.6)
• No

Documentation Checklist

• I have documented all added classes and methods.
• For infrastructure updates, I have updated the developer's guide.
• For significant new features, I have added a section to the getting started guide.

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First-Time Contributor Checklist

• If this is your first contribution, add yourself to pyproject.toml if you wish to do so.

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Additional Notes for Reviewers

Ensure that:

• This PR fully addresses and resolves the referenced issue(s).
• The submitted code is consistent with the merge checklist outlined here.
• The PR covers all relevant aspects according to the development guidelines.
• 100% coverage of the patch is achieved, or justification for a variance is given.

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📚 Documentation preview 📚: https://montepy--968.org.readthedocs.build/en/968/