[MicahGale]

Pull Request Checklist for MontePy

Description

This fixes a few bugs with how UniverseInput handles zeros as brought up in #1051.

Bug in how 0 are transformed back to Jump.

In MCNP 0 and J are interchangeable for Universes. When an explicit 0 was created by 0 2R MontePy tried to coerce it back to a Jump, but not fully. This lead to internal errors with trying to combine it with the repeat shortcut.

This was solved by not coercing these explicit 0s back to Jump.

Dropping trailing Jumps from input.

Usually MCNP lets you drop extra final jumps and implicitly fills out the array. Though as pointed out in #1051 the manual states this is not allowed for a UniverseInput in the data block. These ones must always be explicitly set for every cell, even if just to Jump. To solve this one I just made a mechanism for not allowing the final jump to be dropped by default. This only really shows up with Universes are moved from the cell block where implicit universes are allowed, to the data block, where they are not allowed.

Fixes #1051

---

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 26.
• I have added tests that prove my fix is effective or that my feature works (if applicable).

---

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:
  • Harness used:
  • Reasoning effort:
• No

Documentation Checklist

• I have documented all added classes and methods.
• I have added type hints to all functions as needed.
• I have marked all changes with the .. versionchanged:: or .. versionadded:: directives.

Infrastructure Changes

• For infrastructure updates, I have updated the developer's guide.

Significant features or Behavior changes

• For significant new features, I have added a section to the getting started guide.

---

First-Time Contributor Checklist

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

---

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.

---

📚 Documentation preview 📚: https://montepy--1052.org.readthedocs.build/en/1052/