As a procedural drama centrally interested in the radicalization of a young Muslim boy in Belgium, Adil & Bilall’s “Rebel” pulsates with terrible inevitability. Falling behind at school, with an adored older brother already having made the trip to Syria and a trafficker whispering in his ear, it’s less a question of if Nassim (Amir El Arbi, another tremendous kid actor for Cannes ’22 to tick off) is going to find himself on the Jihadist frontline, but when.