Out-of-bounds Write and Race Condition in metrics-util

In the affected versions of the crate, AtomicBucket unconditionally implements Send/Sync traits. Therefore, users can create a data race to the inner T: !Sync by using the AtomicBucket::data_with() API. Such data races can potentially cause memory corruption or other undefined behavior.

The flaw was fixed in commit 8e6daab by adding appropriate Send/Sync bounds to the Send/Sync impl of struct Block (which is a data type contained inside AtomicBucket).