Stop a run and refund unused credits

Stops a verification run that is still going and returns the credits that were paid for but never used. Addresses already checked keep their results.

Required scope: verification:write.

Safe to call more than once. Only the first call stops the run and refunds; later calls return cancelled: false with credits_refunded: 0 rather than an error, so a retry can never refund twice.

Calling this on a run that already finished is not an error — it reports the run's current state.