Add 2D guess bounds

[stephenworsley]

🚀 Pull Request

Closes #6097

[codecov]

Codecov Report

❌ Patch coverage is 96.10390% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.18%. Comparing base (39dd5eb) to head (060da86).

Files with missing lines	Patch %	Lines
lib/iris/analysis/_grid_angles.py	96.05%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6799      +/-   ##
==========================================
+ Coverage   90.16%   90.18%   +0.01%     
==========================================
  Files          91       91              
  Lines       25026    25102      +76     
  Branches     4695     4706      +11     
==========================================
+ Hits        22565    22638      +73     
- Misses       1683     1685       +2     
- Partials      778      779       +1     

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[pp-mo]

For "review", see stephenworsley#12

[pp-mo]

OK I think this is good to go