WINNIPEG — Casey Mittelstadt is a pretty low-key guy, but he couldn’t contain his excitement. Finally, in his seventh season as a full-time professional hockey player, it was time to find out what the Stanley Cup Playoffs were all about. And it would be hard to say that Mittelstadt did anything but pass his first postseason test with a strong effort. “I think with the energy and the atmosphere overall, I don’t know if I’ve played in a game like that in my career to be honest,” Mittelstadt said.