For Pat Byrne, the idea of retirement seems faintly absurd. In his late thirties, having built a financial services business into what is now Cornmarket, Byrne stepped away financially secure.  “I didn’t really have to do something else,” he says. “Certainly not for a while.” He was 37. It lasted no time at all. “I went into something straightaway, immediately afterwards,” he says. Now, having exited CityJet once more – after a third examinership, a bruising few years of airline consolidation, pandemic aftershocks and aborted mergers – he has gone again, but not quietly. His latest venture is called After-Byrne…