CopyCell lacks bounds on its Send trait allowing for data races

CopyCell<T> is a Cell-like type that is implemented for any type T that
is Copyable. It’s Send trait has no bounds on the contained type.

As not all Copyable types are thread safe, for example non-mutable references
implement the Copy trait, it is possible to send references to types with
interior mutability such as Cell across threads and cause data races.