The number of millionaires in the U.S. jumped during the third quarter of 2024, according to Fidelity Investments. Thanks to a strong stock market surge that is well into its second year, there are now 544,000 401(k)-created millionaires at Fidelity, up from 497,000 in the second quarter. That is a quarter-over-quarter increase of 9.5%. Meanwhile, 418,111 Fidelity investors were IRA-created…