Neatly and purposely divided into three acts — a black screen signals the lag time between each, should the viewer not be ready for the required understanding that things are about to change, and that it’s best to prepare now — Julie Delpy’s fascinating “My Zoe” uses its classic formal structure to tell a thoroughly modern tale. While Delpy’s directorial output thus far has mostly consisted of fizzy rom-coms like her “Two Days” features and the odd historical drama (“The Countess”), “My Zoe” finds the filmmaker and star moving fast into fresh territory. One part domestic drama, one part medical mystery, “My Zoe” subtly spins those two acts into its final segment: a contemporary thriller with morals and medicine on its mind.