[WIP] Variable scaling

[EveCharbie]

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• Have you opened/linked the issue related to your pull request? issue Auto scaling of optimization variables based on bounds #305
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This change is 

[mickaelbegon]

do you check if scaling is always positive?

[pariterre]

Good point
FYI, next time use the "Reviewable" button (as opposed to "Files changed") so we don't sparse the comments across two methods

[EveCharbie]

I think I still need quite a bit of work on this PR, and now I need to work on other things. So I will take a break from this PR. TODO:
iter and next in OptimizationVariablesContrainer
Update biorbd in env + merge bioptim to see if fatigue works (otherwise pariterre will have a look at it)
Test scaling with a granilarity of round numbers like 1, 10, 100 instead of 85 to see if there is a difference
Raise an error of only some scaling are defined (only 'qdot' for example)
Check CVODES behaviour + probably raise an error if used with scaling
remove all ['unscaled'] with appropriate methods

• everything in the review

[pariterre]

Reviewed 33 of 33 files at r5, all commit messages.
Reviewable status: all files reviewed, 26 unresolved discussions (waiting on @EveCharbie and @mickaelbegon)

[codecov]

Codecov Report

Base: 81.60% // Head: 81.47% // Decreases project coverage by -0.12% ⚠️

Coverage data is based on head (fd9a1fb) compared to base (dffe9eb).
Patch coverage: 87.96% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #572      +/-   ##
==========================================
- Coverage   81.60%   81.47%   -0.13%     
==========================================
  Files         104      105       +1     
  Lines       11367    11703     +336     
==========================================
+ Hits         9276     9535     +259     
- Misses       2091     2168      +77     

Impacted Files	Coverage Δ
bioptim/dynamics/ode_solver.py	88.69% <ø> (ø)
...ioptim/examples/getting_started/custom_dynamics.py	88.63% <ø> (-0.26%)	⬇️
...ptim/examples/getting_started/custom_parameters.py	76.92% <ø> (-0.44%)	⬇️
...getting_started/example_continuity_as_objective.py	46.75% <0.00%> (ø)
bioptim/examples/getting_started/pendulum.py	70.37% <ø> (-1.06%)	⬇️
...es/muscle_driven_ocp/muscle_excitations_tracker.py	73.63% <0.00%> (ø)
...mmetrical_torque_driven_ocp/symmetry_by_mapping.py	87.50% <ø> (-0.38%)	⬇️
...examples/torque_driven_ocp/example_soft_contact.py	82.81% <ø> (+1.93%)	⬆️
...amples/torque_driven_ocp/multi_model_by_mapping.py	83.33% <ø> (-0.28%)	⬇️
bioptim/gui/check_conditioning.py	85.59% <63.63%> (ø)
... and 29 more

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[Ipuch]

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