there are technically still two locks
- the Mutex to serialize consurrent updates to the AtomTable
- the RwLock as part of GLOBAL_ATOM_TABLE
the former is the age lock of RESIZE ATOM TABLE in <https://arxiv.org/pdf/1608.00989.pdf>, though we use it for the whole update as we don't match the whole structure and can't reserve an atom slot as is, so we need to also lock concurrent updates without resizing
the later should be uncontendet as we only write AtomTable::new iff the current value is a dangling Weak
