It was hoped SpaceX’s blockbuster June flotation would add rocket boosters to the global IPO market. But four months on, momentum has come crashing back down to earth. Wall Street IPOs have slowed considerably since Elon Musk’s $75bn (£56.7bn) listing, damaging what was once expected to be a quarter chock-full of floats. Smart-ring maker Oura was the latest company to stall its listing just last week, while data centre company SB Energy, petrol station empire EG Group and nuclear energy firm Holtec have all also postponed.…