Tolerant handling of standard_name and dimension coordinate loading

[trexfeathers]

🚀 Pull Request

Description

Closes #6318

To-do

• Raise a warning at the end of loading if anything is present in iris.loading.LOAD_PROBLEMS
• Docstring and UX improvements to iris.loading.LOAD_PROBLEMS.
• Get feedback from reviewer on my approach of adding new routines called build_and_add_*
  • Is the philosophy sound?
  • Is the name too clunky?
• Fix existing unit tests now that I have changed how things work. These failures don't look scary
• Add new tests for iris.loading.LOAD_PROBLEMS and the new warning

Deviation from the original spec

To avoid making too many enhancements to actions.py - which we consider legacy (#6316) - I decided it was better to create new routines for adding elements to the Cube, and house them in helpers.py, with the rest of the non-Pyke code. If the reviewer is happy with this approach, I will rewrite the spec in the issues.

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[trexfeathers]

Here are some to-do's I would appreciate input on.

[trexfeathers]

I forgot to restore the previous state after my doctests are finished.

[codecov]

Codecov Report

Attention: Patch coverage is 96.29630% with 6 lines in your changes missing coverage. Please review.

Project coverage is 89.80%. Comparing base (df5c55f) to head (241a782).
Report is 79 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/iris/fileformats/_nc_load_rules/actions.py	78.57%	2 Missing and 1 partial ⚠️
lib/iris/fileformats/_nc_load_rules/helpers.py	96.62%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6338      +/-   ##
==========================================
+ Coverage   89.78%   89.80%   +0.02%     
==========================================
  Files          90       90              
  Lines       23632    23752     +120     
  Branches     4411     4418       +7     
==========================================
+ Hits        21217    21331     +114     
- Misses       1667     1672       +5     
- Partials      748      749       +1     

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[trexfeathers]

Bit late, but this closes #5171 !

[pp-mo]

Posting what I got so far.
Possibly ongoing, though

[pp-mo]

P.S. with a bit more reading, I see that the "new class" idea for LOAD_PROBLEMS causes a lot of problems.
A dictionary of lists has the advantage that the API needs no explaining !
we should discuss

[pp-mo]

Pretty solid !
Just a few small changes. mostly to tests

All requests resolved

[pp-mo]

All good now !

[trexfeathers]

Thanks @pp-mo!