LOS ANGELES — By age 23, Emma MacTaggart was already noticing how rare her free time was — and how it was seldom screen-free. She was working long hours in investment banking and once she was finally able to log off after work, she would turn to her phone . Along with her roommates, she decided to hunt for a hobby that would replace that habit. They became “hooked” on needlepoint, she said, a practice she had briefly learned from relatives as a child, but one that she hadn’t picked up in years.