Putting the pieces together of a marginalized wife and mother is the objective of “Puzzle,” a sweet, but overwritten character study providing star Kelly Macdonald a too-rare chance to show what the longtime character actor can do with a leading role. And what she does is knock it out of the park.It’s the perfect match between part and performer, taking full advantage of a face that always seems to be looking at the world with a repressed sense of wonder.