The dependent action for src_customers_auths and
dst_customers_auths in the numberlist model has
been changed from restrict_with_error to nullify.
This was to allow for deletion of a numberlist
item even when it has related customer_auths.
Corresponding test cases have been added to ensure
expected behavior.

…y and resilience

The AsyncBatchDestroyJob has been refactored to utilise Rails's `find_in_batches`
method as opposed to a custom SQL query. This proves to make the process of record
deletion both more efficient and more resilient to database inconsistencies.

Previously, records that could not be deleted due to dependencies would raise an
exception, breaking the whole transaction. Now, these records are logged and
skipped over instead. Updates to associated tests have been made to verify and
reflect these changes.