0bd4ee79e0
Add unchecked downcast methods
```rust
impl dyn Any (+ Send + Sync) {
pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T;
pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T;
}
impl<A: Allocator> Box<dyn Any (+ Send + Sync), A> {
pub unsafe fn downcast_unchecked<T: Any>(&self) -> Box<T, A>;
}
```