do_swap_coldkey downgrades perpetual locks to decaying

[gztensor]

When a coldkey swap is performed via do_swap_coldkey(old_coldkey, new_coldkey), all individual Lock rows for old_coldkey are correctly transferred to new_coldkey via swap_coldkey_locks (lock.rs:1327-1374). However, the DecayingLock(coldkey, netuid) flag is never migrated.