make service worker use its own python-wasm scope so it doesn't conflict with other service workers

[williamstein]

We finally have service workers working, e.g., at https://python-wasm.org. However, they just use the / scope. This would presumably conflict with embedding python-wasm into sites that have their own service worker at that scope, e.g., https://cocalc.com has a service worker at /.

That said, it's not clear to me that python-wasm is ever going to be embedded not as an iframe in other web applications, and if it is embedded as an iframe, I think the scope issue goes away. Anyway, recording this here for future thought.