feat: Properly reset simulator

This commit provides the ability to properly reset the simulator
(including invalidating all existing handles). This allows scenes to be
re-created at any point.

src/engine/EventRegistry.ts

@@ -41,6 +41,7 @@ export class EventRegistry {
   private _world: World;
 
   private _timeSinceLastUpdate = 0;
+  private _onDispose: () => void;
 
   /**
    * Create a new EventRegistry and connect it to the provided world
@@ -49,12 +50,27 @@ export class EventRegistry {
   constructor(world: World) {
     // Hook up the event listeners for the physics engine
     // This is for collisions
-    world.on("begin-contact", this.onBeginContact.bind(this));
-    world.on("end-contact", this.onEndContact.bind(this));
+    const onBeginContantFunc: (
+      contact: Contact
+    ) => void = this.onBeginContact.bind(this);
+    const onEndContantFunc: (contact: Contact) => void = this.onEndContact.bind(
+      this
+    );
+    world.on("begin-contact", onBeginContantFunc);
+    world.on("end-contact", onEndContantFunc);
+
+    this._onDispose = () => {
+      world.off("begin-contact", onBeginContantFunc);
+      world.off("end-contact", onEndContantFunc);
+    };
 
     this._world = world;
   }
 
+  dispose(): void {
+    this._onDispose();
+  }
+
   // World event handlers
   /**
    * Event handler when a collision begins to occur (shapes overlapping)

src/engine/HandleRegistry.ts

@@ -0,0 +1,33 @@
+export class HandleRegistry {
+  private _invalidationCallbacks: Map<string, () => void> = new Map<
+    string,
+    () => void
+  >();
+
+  registerHandle(objectGuid: string, invalidateCb: () => void): void {
+    this._invalidationCallbacks.set(objectGuid, invalidateCb);
+  }
+
+  invalidateHandle(guid: string): void {
+    if (this._invalidationCallbacks.has(guid)) {
+      const invalidationCb = this._invalidationCallbacks.get(guid);
+      invalidationCb();
+    }
+  }
+
+  deleteHandle(guid: string): void {
+    this.invalidateHandle(guid);
+    this._invalidationCallbacks.delete(guid);
+  }
+
+  invalidateAllHandles(): void {
+    this._invalidationCallbacks.forEach((invalidationCb) => {
+      invalidationCb();
+    });
+  }
+
+  deleteAllHandles(): void {
+    this.invalidateAllHandles();
+    this._invalidationCallbacks.clear();
+  }
+}