Omar Marques | Lightrocket | Getty ImagesApple is struggling to squeeze growth out of its flagship iPhone unit, but its profit margin keeps going up thanks to a flourishing services business.In its fiscal first-quarter earnings report on Thursday, Apple reported a gross margin — the profit left after accounting for the cost of goods sold — of 46.9%. That's the highest on record, surpassing the 46.6% margin the company record in the period ending March 2024.For Apple, services includes App Store ...