Mescal, the terrific Irish actor of “Aftersun” and “All of Us Strangers,” smoothly steps into a blockbuster arena for the first time. “This one is interesting,” says Macrinus, eyeing him for the first time. Mescal’s Lucius is vengeful — the Roman army kills his warrior wife in the Numidia battle. “Rage pours out of you like milk,” Macrinus says, admiringly. The glint of mischief in Mescal’s eyes gives Lucius a little more character than your average revenge-seeking gladiator.