WIP Codim coupling

[RemDelaporteMathurin]

Description

Summary

Related Issues

Motivation and Context

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 🔨 Code refactoring (no functional changes, no API changes)
• 📝 Documentation update
• ✅ Test update (adding missing tests or correcting existing tests)
• 🔧 Build/CI configuration change

Testing

• All existing tests pass locally (pytest)
• I have added new tests that prove my fix is effective or that my feature works

Code Quality Checklist

• My code follows the code style of this project (Ruff formatted: ruff format .)
• My code passes linting checks (ruff check .)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

Documentation

• I have updated the documentation accordingly (if applicable)
• I have added docstrings to new functions/classes following the project conventions

Breaking Changes

Screenshots/Examples

Additional Notes

[codecov]

Codecov Report

❌ Patch coverage is 95.63863% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.16%. Comparing base (23284d2) to head (283389b).

Files with missing lines	Patch %	Lines
src/festim/mixed_dimensional_assembly.py	92.78%	7 Missing ⚠️
src/festim/hydrogen_transport_problem.py	96.77%	4 Missing ⚠️
src/festim/problem.py	90.00%	1 Missing ⚠️
src/festim/subdomain/interface.py	92.85%	1 Missing ⚠️
src/festim/subdomain/volume_subdomain.py	97.95%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1216      +/-   ##
==========================================
- Coverage   95.19%   95.16%   -0.03%     
==========================================
  Files          53       54       +1     
  Lines        3952     4221     +269     
==========================================
+ Hits         3762     4017     +255     
- Misses        190      204      +14     

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[RemDelaporteMathurin]

@jorgensd this is the PR of the codim implementation in FESTIM (currently limited to codim <=1 but I don't see why we couldn't do codim 2).

Note that it doesn't use MixedFunctionSpace. The scope currently limits to coupling on outer boundaries not internal ones, maybe that's why we can do it without? Keen to have your opinion on this first draft