Feature: add neighbor subface helper

[dutkalex]

Describe your changes here:
Implements #2215

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.50%. Comparing base (4a82a3b) to head (9a570df).

Files with missing lines	Patch %	Lines
src/t8_forest/t8_forest.cxx	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2216      +/-   ##
==========================================
- Coverage   82.57%   82.50%   -0.07%     
==========================================
  Files         116      116              
  Lines       18553    18568      +15     
==========================================
  Hits        15320    15320              
- Misses       3233     3248      +15     

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[spenke91]

Thank you very much @dutkalex for another great contribution! :-) I am sorry it took us so long to reply...
I mostly have suggestions regarding variable names and code comments (which, I know, not everybody loves as much as I do 🤓 ). Aside from that, I only have a question regarding the hard-coded 4.

[dutkalex]

Thank you very much @dutkalex for another great contribution! :-) I am sorry it took us so long to reply...

No worries @spenke91. Thank you for taking the time, I know you guys have a lot on your plate.

I mostly have suggestions regarding variable names and code comments (which, I know, not everybody loves as much as I do 🤓 ). Aside from that, I only have a question regarding the hard-coded 4.

I get it, I often say that getting the compiler to understand the code is the easy part and that the real challenge it to write code that humans can comprehend 😉. I have either committed your suggestions directly, or answered your comments/questions to get your opinion. Let me know what you think and I'll revise the code accordingly.

[spenke91]

Thanks a lot for your comments and replies!

[spenke91]

Thanks a lot @dutkalex for this contribution! 👍

[spenke91]

The doxygen workflow is failing due to a minor typo...

[spenke91]

@dutkalex The failing doxygen workflow has nothing to do with your PR specifically. We have a rather unstable setup there which I will fix in the next days (#2331). Until then, I tried restarting the workflows.