Refactoring for interface discontinuities

[RemDelaporteMathurin]

Proposed changes

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request. If it fixes a bug or resolves a feature request, be sure to link to that issue.

Types of changes

What types of changes does your code introduce to FESTIM?

• Bugfix (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
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Black formatted
• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov]

Codecov Report

Attention: Patch coverage is 87.03704% with 21 lines in your changes missing coverage. Please review.

Project coverage is 96.00%. Comparing base (96d62ff) to head (a23d5e6).

Files with missing lines	Patch %	Lines
src/festim/hydrogen_transport_problem.py	86.36%	21 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           fenicsx     #944      +/-   ##
===========================================
- Coverage    96.02%   96.00%   -0.02%     
===========================================
  Files           45       44       -1     
  Lines         2439     2402      -37     
===========================================
- Hits          2342     2306      -36     
+ Misses          97       96       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[RemDelaporteMathurin]

Making use of FEniCS/dolfinx#3450 we should be able to simplify the form creation using extract_blocks. Need to chat with @jorgensd to see how we can implement this