How did ref handling change in React 19 — why was forwardRef needed before, what does the new ref-as-prop model enable, and what is the new ref cleanup API?

Imagine you have a toy box and you want to give your friend a special toy. Before, you had to wrap it in a special paper (forwardRef) to pass it. Now, you can just hand it over directly. Also, if you borrow a toy, you can now say 'I'm done with it' so the toy box knows to clean up.