Make MeshCoords immutable and sync updates with the attached mesh

[ESadek-MO]

🚀 Pull Request

Description

Closes #4757, continues #6125.

This pull request aims to make MeshCoords immutable, and when it's corresponding Mesh updates, for the MeshCoord to refresh its Points, Bounds, and Metadata from the Mesh.

Notes to self

• First problem, where node had no bounds, has been solved.
• Next problem is that bounds aren't being rendered in the cml (and presumably, don't exist). There wasa thread to pull, in that bounds is set to an error message about bounds_dm, but it seems like that's a red herring, and is solved within __init__.
• There's a chance this only solves another 10 or so errors, but progress is progress

[codecov]

Codecov Report

❌ Patch coverage is 90.65421% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.89%. Comparing base (4e92a5e) to head (3997560).
⚠️ Report is 134 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/iris/mesh/components.py	90.38%	13 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6405      +/-   ##
==========================================
+ Coverage   89.88%   89.89%   +0.01%     
==========================================
  Files          90       90              
  Lines       23945    24123     +178     
  Branches     4467     4489      +22     
==========================================
+ Hits        21522    21685     +163     
- Misses       1670     1679       +9     
- Partials      753      759       +6     

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[stephenworsley]

Looking good! Here's some comments from the code itself, I'll go through the tests next. The timestamp stuff looks like it should do the job now, I think mostly I just have virable name and documentation quibbles.

[stephenworsley]

Looking good, I believe these are the last things I can find to request changes on, after this it should be good to merge!

[pp-mo]

Thanks @ESadek-MO @stephenworsley
Just to confirm, I'm looking at this now, looks very close but I need a bit longer to think ....
Hopefully I will just merge later today.

I think it has now all been done

[pp-mo]

Now looking all ok