Adaptive timestepping

[kaelyndunnell]

Proposed changes

Adds new features (milestones, maximum stepsize) to adaptive timestepping in fenicsx in line with Issues #913 and #912.

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 97.80%. Comparing base (7a770bc) to head (6b68b91).
Report is 74 commits behind head on fenicsx.

Additional details and impacted files

@@             Coverage Diff             @@
##           fenicsx     #916      +/-   ##
===========================================
+ Coverage    97.76%   97.80%   +0.04%     
===========================================
  Files           44       44              
  Lines         2099     2142      +43     
===========================================
+ Hits          2052     2095      +43     
  Misses          47       47              

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[RemDelaporteMathurin]

Thanks @kaelyndunnell that's super needed! 🚀

I think there is an edge case that you haven't tested (see comments below).

Also needs tests for milestones.