There are two films in Julie Delpy’s ambitious, sharply-made but unbalanced “My Zoe.” There’s the scabrous relationship melodrama, about bitter exes sharing custody of a beloved child, which contains the story’s most potent emotions. And there’s the sci-fi-inflected ethical-dilemma grief movie, which houses its most provocative ideas. Both have much to recommend them, not least Delpy’s lithe filmmaking, polished over her now seven features to a consummate, unobtrusive sheen. But the transition between the two halves or, more appropriately, the cloning of the second from a tissue sample of the first, plays awkwardly, and suggests that Delpy’s screenwriting, while studded with moments of shrewd insight, as yet lags some way…