Implemented clear for material

[MicahGale]

Pull Request Checklist for MontePy

Description

This implements clear for Material. This also fixes a bug where sometimes you would get garbled materials like m1 1001.80c 0.68016.80c 0.3. This is due to the last edge leaf of the syntax tree having no space or no padding. This fixes this by every time a nuclide or default library is added it checks if there is an existing space, and if not it adds a new line (and the requisite spaces).

Fixes #665, fixes #667, fixes #666.

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

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Documentation Checklist

• I have documented all added classes and methods.

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Additional Notes for Reviewers

Ensure that:

• 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--668.org.readthedocs.build/en/668/

[MicahGale]

I don't like that this is 92% patch coverage.

[tjlaboss]

pathway not tested

[MicahGale]

Part of this path is only used with a shortcut phrase. I'm not sure if this is worth testing.

[MicahGale]

Need to still fix #667.