Fix tiny timestep bug

[gabriele-ferrero]

Proposed changes

When starting to solve a model, some initial stepsize can be required. Sometimes the adaptive timesteps becomes very small at the beginning of a simulation. In these cases, the message output in festim is 0.0 s. With this change, we can see tiny timesteps in the scientific format (eg 1E-9 s).

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
• [X ] I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (2847817) 99.07% compared to head (56938e1) 99.07%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #580      +/-   ##
==========================================
- Coverage   99.07%   99.07%   -0.01%     
==========================================
  Files          56       56              
  Lines        2054     2053       -1     
==========================================
- Hits         2035     2034       -1     
  Misses         19       19              

Files	Coverage Δ
festim/generic_simulation.py	100.00% <100.00%> (ø)

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[RemDelaporteMathurin]

Thank you very much @gabriele-ferrero for this fix!