Setting `pixels_per_meter` doesn't seem to affect the physics scale

I think I might be misunderstanding what this value does. When running the `boxes2` example, there seems to be no difference between adjusting the `pixels_per_meter` value. I have tried using a value of `1.0`, `100.0` (default), and `10000.0` and the simulations seem to run exactly the same.

From [Common Mistakes: Why is Everything Moving in Slow Motion](https://rapier.rs/docs/user_guides/bevy_plugin/common_mistakes#why-is-everything-moving-in-slow-motion) docs, I got the impression that the `pixels_per_meter` constructor would adjust the simulation scale. I was expecting that a value of `1.0` would cause the boxes to fall a lot slower (since they'd be bigger and have further to fall) and I was expecting a value of `10000.0` to cause the boxes to fall a lot faster, since they'd be smaller and much closer to the ground.