feat(rapier_testbed): autosave testbed configuration + add support for per-example settings (#799)

* feat(rapier_testbed): autosave testbed configuration + add support for per-example parameters

* feat(rapier_testbed): also save the camera position

* feat(rapier_testbed): improve ergonomics of example-specific settings

* chore: cargo fmt

* chore(rapier_testbed): small UI ergonomics improvement

* chore(rapier_testbed): clippy fixes

src_testbed/camera2d.rs

@@ -9,7 +9,7 @@ use bevy::render::camera::Camera;
 
 const LINE_TO_PIXEL_RATIO: f32 = 0.1;
 
-#[derive(Component)]
+#[derive(Component, PartialEq, Debug, Clone, serde::Serialize, serde::Deserialize)]
 pub struct OrbitCamera {
     pub zoom: f32,
     pub center: Vec3,