MagneticConstraintSet - remove and avoid a couple of pertinent deepcopies

[geograham]

Description

Constraints/Targets not updating - deepcopy in dummy eq set up, and if deepcopy of eq used between setting up optimisation problem and the Picard iterator resulted in disconnection.

Interface Changes

PicardIterator no longer takes eq as input. Does not need to, as we have the COP (with relevant eq) as input.

Checklist

I confirm that I have completed the following checks:

• Tests run locally and pass pytest tests --reactor
• Code quality checks run locally and pass pre-commit run --from-ref develop --to-ref HEAD
• Documentation built locally and checked sphinx-build -W documentation/source documentation/build

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.68%. Comparing base (447515f) to head (01bc3af).

Files with missing lines	Patch %	Lines
bluemira/equilibria/run.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4170      +/-   ##
===========================================
- Coverage    78.95%   78.68%   -0.28%     
===========================================
  Files          244      244              
  Lines        29322    29320       -2     
===========================================
- Hits         23150    23069      -81     
- Misses        6172     6251      +79     

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[github-actions]

⚠️ Warning Report

Found 0 new warnings, 0 fixed warnings. 🎉

All warnings (1)

On collect

• /home/runner/work/bluemira/bluemira/bluemira/codes/openmc/solver.py:60: DeprecationWarning: In 3.13 the default auto()/generate_next_value will require all values to be sortable and support adding +1 and the value returned will be the largest value in the enum incremented by 1