Add geometry functions: curvature, frenet_transform, jerk

[Kotakku]

baglab.geometry — additional functions

General-purpose geometric computations, same category as existing cumulative_distance, pose_error, etc.

Function	Purpose	Priority
curvature(path)	Path curvature computation	Medium
frenet_transform(point, ref_path)	Frenet coordinate transform (s, d)	Medium
jerk(velocity, t)	Jerk computation (convenience wrapper over double signal.diff)	Medium