properly sync intersectObjects array in useFollowCam hook

[hichemfantar]

This pull request adds child event listeners in the useFollowCam hook. The useFollowCam hook now listens for "childadded" and "childremoved" events in the scene. When a child is added or removed, the render state is updated, triggering a re-render. This ensures that the intersectObjects array is updated correctly when children are added or removed.

the problem is that the useFollowCam relies on component render, so if you add or remove elements that aren't at the level ecctrl was invoked then it won't rerender ecctrl and useFollowCam wouldn't update the intersectObjects array

with this fix, intersectObjects array will be updated when the ecctrl component rerenders and when objects are added or removed the scene.

i'm also thinking about completely getting rid of recomputing on every render and instead rely solely on the event listeners and add or remove elements from the array respectively.

the current paradigm with recompute intersectObjects array on every render seems very wasteful in terms of performance.

closes #117