PHILADELPHIA — Only four weeks ago, in a home win against the Philadelphia 76ers, the Luka Dončić-Kyrie Irving partnership looked nearly invincible, poised to become one of the NBA’s most menacing duos, prepared to lead Dallas to a comfortable playoff seed and perhaps even a feisty postseason run that set up the future. Just four weeks ago, those two combined for 82 points, and this team was brimming with optimism. Advertisement Four weeks later, hardly any remains. Dallas lost 116-108 to the same Philadelphia 76ers on Wednesday, a defeat that sunk the Mavericks to a 37-40 record that leaves them…