When an auth file is deleted and re-created with the same path/ID, the
new auth could inherit stale ModelStates (cooldown/backoff) from the
previously disabled entry, preventing it from being routed.
Gate runtime state inheritance (ModelStates, LastRefreshedAt,
NextRefreshAfter) on both existing and incoming auth being non-disabled
in Manager.Update and Service.applyCoreAuthAddOrUpdate.
Closes#2061
