Does the current system permit atomic accesses to values of type T?

This is typically true for ref values and for small primitive types
such as `i32`, `f64`, etc. while this is typically not the case for
more complex types such as `point(x,y i64)`.

For mutable fields created by heirs of `concur.atomic_mutate`, it will
not be possible to use `get_racy` or `put_racy` unless they are
performed on a type where these accesses are atomic.