[RTR] split final MHE save

[Ipuch]

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This change is 

[Ipuch]

won't work yet because, when we move from one frame to another it make no sens to same this.
Only if frame to move is superior to 1, or only for multicyclic.

[codecov]

Codecov Report

Base: 81.47% // Head: 81.54% // Increases project coverage by +0.06% 🎉

Coverage data is based on head (a4b80e6) compared to base (fd9a1fb).
Patch coverage: 97.29% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #592      +/-   ##
==========================================
+ Coverage   81.47%   81.54%   +0.06%     
==========================================
  Files         105      105              
  Lines       11703    11739      +36     
==========================================
+ Hits         9535     9572      +37     
+ Misses       2168     2167       -1     

Impacted Files	Coverage Δ
bioptim/examples/moving_horizon_estimation/mhe.py	50.87% <0.00%> (ø)
bioptim/interfaces/solve_ivp_interface.py	96.77% <100.00%> (ø)
...ptim/optimization/receding_horizon_optimization.py	94.94% <100.00%> (+1.00%)	⬆️
bioptim/optimization/solution.py	83.58% <100.00%> (+0.02%)	⬆️
bioptim/dynamics/configure_problem.py	90.97% <0.00%> (+0.04%)	⬆️
bioptim/dynamics/dynamics_functions.py	94.18% <0.00%> (+0.16%)	⬆️

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[pariterre]

out = []
if get_all_interations:
out.append(...)
if ...:
out.append(...)

[Ipuch]

Done.

[Ipuch]

@pariterre