Struggling Polestar faces some serious financial challenges now that Volvo, its Swedish parent, plans to cut off funding for the battery-electric startup. It’s the latest sign of retrenchment by the auto industry as the rapid growth of EV sales has started to flatten out. Volvo itself continues to move forward with plans to become an all-electric brand by decade’s end. Investors applauded the move — and Volvo’s stronger than expected earnings.