MMS testing

[jhdark]

Proposed changes

MMS testing! This PR starts to build up an MMS testing suite for vigorous verification testing. I've adapted the tests in fenicsx tutorial.

This PR provides the first version of how system tests can be implemented in fenicsx, however a more sophisticated infrastructure of MMS testing will be implemented in the future!

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

All modified and coverable lines are covered by tests ✅

Project coverage is 99.24%. Comparing base (ec46ff2) to head (0ba836b).

Additional details and impacted files

@@             Coverage Diff             @@
##           fenicsx     #721      +/-   ##
===========================================
+ Coverage    99.15%   99.24%   +0.08%     
===========================================
  Files           26       26              
  Lines         1183     1185       +2     
===========================================
+ Hits          1173     1176       +3     
+ Misses          10        9       -1     

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[RemDelaporteMathurin]

Thanks for this. We will have to work on homogenising the MMS testing architecture later