Rurik Bradbury arrives at the podcast studio wearing his business.  A blinking band on one arm and a sticky patch on the back of the other.  The chief executive of Limbo, Bradbury, and his start-up are among the latest cohort of biohackers, who espouse the use of wearable trackers to optimise health and longevity, and to lose weight.  It is another step forward in this era of bodily surveillance, which sees corporeal data wonks tracking their sleep, steps, heart rates, calories, and periods.  The metric Limbo uses is continuous glucose monitoring (CGM) and the goal is to keep it at…