Offer nicer streaming APIs

[lemonmade]

• [ ] Optionally: add a two-chunk stream that renders the entry assets, then return the app chunk
• [ ] Options for streaming the rendering of Suspense boundaries (maybe, not totally sold on this, since it relies on HTML reordering on the client)
• [ ] Add APIs for progressive serializations

const browser = new Browser();

const serialization = await browser.serializations.waitUntil('serialized-id', {
  signal: abortController.signal,
});
// ...

const stream = browser.serializations.stream('serialized-id', {
  signal: abourtController.signal,
});

for await (const serialized of stream) {
  // ...
}