Add 2D guess bounds

[stephenworsley]

🚀 Pull Request

Closes #6097

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.12%. Comparing base (8f0b62b) to head (84815af).
⚠️ Report is 143 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/iris/analysis/_grid_angles.py	95.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6799      +/-   ##
==========================================
- Coverage   90.29%   90.12%   -0.17%     
==========================================
  Files          91       91              
  Lines       24465    24972     +507     
  Branches     4568     4681     +113     
==========================================
+ Hits        22090    22506     +416     
- Misses       1607     1686      +79     
- Partials      768      780      +12     

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