Before a mid-May practice at the Mercury’s facility in Scottsdale, Ariz., Tina Charles worked through her offensive repertoire. Or, rather, she worked through what portion of it she could, in the space of a half hour. Charles possesses her sport’s thickest catalog of low-post maneuvers: pivots and reverse-pivots, shoulder-shimmy misdirects, up-and-unders and step-throughs and one-footed fadeaways, lately buttressed by a quickening handle and smooth three-point stroke. While Diana Taurasi and Skylar Diggins-Smith, two tentpoles of the Mercury team that made last year’s WNBA Finals, played a shooting game on the far court, Charles sweated on the near one, sidestepping into threes and spinning jump hooks from her fingertips.