By Manya Saini (Reuters) -Electric aircraft maker Beta Technologies filed for an initial public offering in the United States on Monday, the latest company to join the rush to tap a record-breaking bull run in the equity market. Easing trade tensions, robust stock markets and pent-up investor demand have combined to create one of the busiest windows for listings in years, with technology, aerospace and green energy firms leading the charge. Beta Technologies designs, manufactures and sells high-performa ...