Implement `Send` and `Sync` for `ThinBox<T>` Just like `Box<T>`, `ThinBox<T>` owns its data on the heap, so it should implement `Send` and `Sync` when `T` does. This extends tracking issue #92791.
Implement `Send` and `Sync` for `ThinBox<T>` Just like `Box<T>`, `ThinBox<T>` owns its data on the heap, so it should implement `Send` and `Sync` when `T` does. This extends tracking issue #92791.