Sometimes you hear a singer who embodies a role so completely that it’s hard to imagine her in anything else. That’s how I felt about the wonderful mezzo Aigul Akhmetshina, who’s singing the title role in the Met’s new production of Bizet’s CARMEN, which I saw at its second performance. Her portrayal was as full-bodied as her voice and she sizzled, filling up the stage as much as one can imagine. It’s little surprise that she’s considered the Carmen of the moment, having appeared in seven other productions (with two to come).