When asked if this lavish historical epic, about an early-20th-century fighter– turned–Chinese hero, really does mark his farewell to the balletic brawling that made him an action-film icon, Jet Li pauses and launches into a thoughtful explanation of kung fu. Is he waxing philosophical — or deftly evading? Not that a 43-year-old martial artiste who's endured multiple broken bones in a long and aspirin-filled career shouldn't be thinking retirement. So what's next for him? ''The 'J and J' movie,'' he begins. Pardon? ''Jet and Jackie Chan,'' he explains. Sounds like somebody should be stocking up on painkillers...