Fix getNeighboringCellIndices

[mgjarrett]

What is the change?

The staticmethod to get neighboring cell indices in a StructuredGrid is implemented incorrectly:

https://github.com/terrapower/armi/blob/14c951a05214154a1e6bfb43c728aa714084cea7/armi/reactor/grids/structuredgrid.py#L379-L382

It looks like a typo; there is a 1 where there should be an i.

Also, a unit test is added to cover this function.

Why is the change being made?

The previous implementation is incorrect.

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Checklist

• [x] This PR has only one purpose or idea.
• [x] Tests have been added/updated to verify that the new/changed code works.

• [x] The code style follows good practices.
• [x] The commit message(s) follow good practices.

• [x] The release notes (location doc/release/0.X.rst) are up-to-date with any important changes.
• [x] The documentation is still up-to-date in the doc folder.
• [x] If any requirements were affected, mention it in the release notes.
• [x] The dependencies are still up-to-date in pyproject.toml.

[opotowsky]

Whoah nice catch! Will this affect internal integration testing?

[john-science]

Whoah nice catch! Will this affect internal integration testing?

Michael did that testing. This is ready for prime time.

[drewj-usnctech]

FWIW this existed prior to the refactoring in #1373

https://github.com/terrapower/armi/blob/da28372a240e80418139d1069317f546af9bcd8d/armi/reactor/grids.py#L929-L932

My intention there was just to copy code off Grid and move it to StructuredGrid. But I'm glad it has been discovered and fixed!

[mgjarrett]

Ah, I didn't look that closely. Didn't see the side-by-side diff because it was moved to a new file.

It looks like this had been around for over 5 years (probably much longer). I guess this shows how little exercise the Cartesian code gets.