Repair MLX CPU scan, sort, and argsort evaluation for zero-length axes while preserving allocation lifecycle…

Repair MLX CPU scan, sort, and argsort evaluation for zero-length axes while preserving allocation lifecycle…: a task in MiMo-V2.6-RL-harbor-terminal: MiMo-V2.6-RL Terminal (Harbor) (Harbor dataset). Repair MLX's existing CPU backend handling for zero-length axes in scan, sort, and argsort.