refactored nested for loops for readability

[shimwell]

Description

Just taking a peak at the code and this jumped out at me and I couldn't resist attempting to refactor this 11 level nested for loop so that it indented the code less

Fixes # (issue)

No issues

Additional dependencies introduced.

• import itertools but this is included in the python standard library

Type of change

Please select what type of change this is.

• [x] cleaner code

Testing

Sorry I've not added any extra tests, I guess it is covered by existing tests but sorry I've not checked

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] General testing
  • [ ] New and existing unit tests pass locally with my changes
  • [ ] Coverage is >80%

[dodu94]

@AlbertoBittes is currently working on removing all MCNP parsing logic from JADE and introduce F4Enix dependencies instead. Please Alberto put these changes in F4Enix directly, in the meantime I will live this PR open until you do so we do not forget. Thanks Jonathan