Use Arc Instead of Vec

helpful video, just learning rust so I'm not as familiar with Arc yet. also, really glad to see other creators using manim (the data viz library by 3blue1brown), it makes good looking animations.

Title should really be Arc<[T]> at first I was like Arc<T> makes no sense.

It's a great video though. It'd be nice if the compiler / clippy could detect entirely non-mutable uses of data structures that could be switched like this.