/// See [`Exclusive`](https://github.com/rust-lang/rust/issues/98407) for stdlib's upcoming implementation,
/// which should replace this one entirely.
///
/// Provides a wrapper that allows making any type unconditionally [`Sync`] by only providing mutable access.
// SAFETY: `Sync` only allows multithreaded access via immutable reference.
// As `SyncCell` requires an exclusive reference to access the wrapped value,
// marking this type as `Sync` does not actually allow threaded access to the inner value.
unsafe