flutter_scene_box3d 0.2.0

• BREAKING: the backend now implements the PhysicsSimulation contract from package:scene; the runtime dependency moved from flutter_scene to scene.
• BREAKING: removed the Box3dRigidBody, Box3dCollider, and Box3dJoint types; construct only Box3dPhysicsWorld and attach flutter_scene's generic RigidBody, Collider, and joint components.
• BREAKING: wrap the world in flutter_scene's PhysicsWorld now, PhysicsWorld(Box3dPhysicsWorld(...)), instead of adding the concrete components directly.
• Require box3d ^0.1.1 for the Android native load fix.