doc: using MultipleShooting in the manual for the unstable pendulum system

[franckgaga]

Added a simple test with OSQP + MultipleShooting on the linearized inverted pendulum model.

OSQP + MultipleShooting gives similar solutions to DAQP + SingleShooting. Good news! It's consistent with the optimal control theory, that is:

• MultipleShooting is more adapted to unstable systems, but it needs a solver that exploit sparsity like OSQP.
• Active-set methods like in DAQP are more robust to unstable systems for optimal control problem in its dense formulation.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.60%. Comparing base (77163a7) to head (adf25bb).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

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  Coverage   98.60%   98.60%           
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  Files          26       26           
  Lines        4435     4435           
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  Hits         4373     4373           
  Misses         62       62           

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