Add set_chase_camera! helper function for 3rd-person object tracking …

[rainerrodrigues]

Description

This PR addresses the highly requested features from Issue #116 (Camera that follows the object) and Issue #205.

While MeshCat supports Trackball controls to look at an object, there hasn't been a built-in Julia-side way to physically lock the camera's position to a moving target (like a 3rd-person chase camera for drones or robotic end-effectors).

This PR introduces set_chase_camera!, a lightweight helper function that composes a target's transformation matrix with a user-defined camera offset, and applies it directly to the vis["/Cameras/default"] path.

Example Usage inside a simulation loop:

# Move the drone
drone_tform = Translation(x, y, z) ∘ LinearMap(RotZ(heading))
settransform!(vis[:drone], drone_tform)

# Lock the camera 4 units behind and 2 units above the drone
set_chase_camera!(vis, drone_tform, offset=Translation(-4.0, 0.0, 2.0))