Update the testbed to use PhysicsHooks.

src/pipeline/mod.rs

@@ -2,10 +2,14 @@
 
 pub use collision_pipeline::CollisionPipeline;
 pub use event_handler::{ChannelEventCollector, EventHandler};
+pub use physics_hooks::{
+    ContactModificationContext, PairFilterContext, PhysicsHooks, PhysicsHooksFlags,
+};
 pub use physics_pipeline::PhysicsPipeline;
 pub use query_pipeline::QueryPipeline;
 
 mod collision_pipeline;
 mod event_handler;
+mod physics_hooks;
 mod physics_pipeline;
 mod query_pipeline;