Fix many memory leaks

VisualPinball.Unity/VisualPinball.Unity/Common/LazyInit.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace VisualPinball.Unity
+{
+	public class LazyInit<T>
+	{
+		private bool isInitialized = false;
+		private T value;
+		public ref T Ref
+		{
+			get
+			{
+				if (!isInitialized) {
+					isInitialized = true;
+					value = constructor();
+				}
+				return ref value;
+			}
+		}
+
+		private readonly Func<T> constructor;
+
+		public LazyInit(Func<T> constructor)
+		{
+			this.constructor = constructor;
+		}
+	}
+}

VisualPinball.Unity/VisualPinball.Unity/Game/PhysicsCycle.cs

@@ -44,11 +44,11 @@ internal void Simulate(ref PhysicsState state, in AABB playfieldBounds, ref Nati
 
 			// create octree of ball-to-ball collision
 			// it's okay to have this code outside of the inner loop, as the ball hitrects already include the maximum distance they can travel in that timespan
-			var ballOctree = PhysicsDynamicBroadPhase.CreateOctree(ref state.Balls, in playfieldBounds);
+			using var ballOctree = PhysicsDynamicBroadPhase.CreateOctree(ref state.Balls, in playfieldBounds);
 
 			// create octree of kinematic-to-ball collision
 			PhysicsKinematicBroadPhase.TransformColliders(ref state);
-			var kineticOctree = PhysicsKinematicBroadPhase.CreateOctree(ref state.KinematicColliders, in playfieldBounds);
+			using var kineticOctree = PhysicsKinematicBroadPhase.CreateOctree(ref state.KinematicColliders, in playfieldBounds);
 
 			while (dTime > 0) {