SEATTLE — When his last swing of the bat was finished, one of the handful that didn’t produce a home run, an exhausted Julio Rodriguez, flung his black and yellow custom bat into the air, and looked at T-Mobile Park crowd, all standing, all cheering and all in awe of what they’d just seen. In his first round matchup against two-time champion Pete Alonso, he’d just set a new derby record with 41…