What is the most effective way to structure a Zwift interval training session to target specific physiological adaptations, such as increasing lactate threshold or improving anaerobic capacity, and how can you use Zwifts built-in training plans, workouts, and analytics tools to optimize your training and track your progress over time, while also avoiding plateaus and preventing overtraining or injury, and what are some best practices for incorporating Zwift into a well-rounded training program that includes outdoor riding and other forms of cross-training, and how can you use Zwifts social features, such as group workouts and virtual racing, to add variety and motivation to your training routine, and what are some common mistakes to avoid when using Zwift for interval training, and how can you use Zwifts data and analytics to inform your training decisions and make adjustments to your training plan as needed.