A shadow fleet is quietly swelling across the world’s oceans, packed with sanctioned barrels from Russia, Iran, and Venezuela. For now, those tankers have kept to the sidelines of the global market—but the sheer scale of crude idling offshore could soon jolt prices, depending on whether the oil ever finds a buyer. Of course, Russia's oil shipments abroad have been in the spotlight over the past few weeks, as the media rush to report how Chinese and Indian buyers are canceling orders and switching to Middle Eastern and American oil until…