If AtomicValue[T] is used with a T that is an interface kind,
then Store may panic if different concret types are ever stored.
Fix this by always wrapping in a concrete type.
Technically, this is only needed if T is an interface kind,
but there is no harm in doing it also for non-interface kinds.
Updates #cleanup
Signed-off-by: Joe Tsai <joetsai@digital-static.net>