crocoddyl: Feasibility-Driven Differential Dynamic Programming for Optimal Control

Reproduced the core mathematical formulation of the crocoddyl solver isomorphically: Riccati backward sweep, LM regularization, and gap contraction expansion. On a large-amplitude cart-pole swing-up task, a three-way comparison was conducted; FeasShoot required fewer than 30% of the iterations of the shooting method, and regularization remained frozen.