Add autodismissal time-to-live progress bar

This is really cool, ui.dev's newsletter brought me here!

I'm just missing a few features so I'll be making a few issues to keep track of that, starting with this one:

Feature request

A time-to-live progress bar would make the UX of autodismissal of toasts after a specified duration significantly clearer. The bar should be full when the toast appears and empty out until the specified toast duration passes (when the toast is autodismissed).