The guy who invented Amazon Prime disappeared for six years. He came back this week with $250 million and a factory that turns lines of code into tiny working machines. Type different code, a different machine comes out the other end. That sounds fake. Here's why it took six years. A chip fab is the most precise factory humans have ever built, and it makes exactly one kind of thing. Flat silicon that processes information. The moment you want moving parts, multiple materials, or real 3D…