Refactor dynamics calculations to incorporate rear axle ratio to improved steering and yaw dynamics

[Victorbares]

This commit updates the drive dynamics to consistently account for the rear axle ratio in the bicycle model.

Summary:

• Updates jerk-model position and velocity integration so motion follows heading + beta.
• Slightly tightens random training spawn width from 3.0m to 2.7m to match truck size and make the off-road performances similar to slipless models.

[eugenevinitsky]

Awesome. Can you say more about what the goal of this PR is?

[Victorbares]

The goal of this PR is to account for the side slip angle in the bicycle model.
The point of reference (sim_x,sim_y) of our agents is the center of the bbox. So our current bicycle model make the vehicle rotate around the center of the bbox which is not "coherent" for a real vehicle.
The goal of the PR is to have a more "realistic" bicycle model.
This can be useful to get the difference of equations depending of the reference point https://dingyan89.medium.com/simple-understanding-of-kinematic-bicycle-model-81cac6420357