Codex/pinocchio model backend

[mickaelbegon]

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This change is 

[pariterre]

NOTE: This PR must be rebased to earlier version of bioptim to be mergeable.

The class is created, but nothing is actually really done and is probably not working as is expected to inherit from the StateDynamics but does not.
The tests are currently minimal and should greatly be augmented

[pariterre]

Rebased and rePRed in #1055