ai/rsc: Make RSC streamable utils chainable

[shuding]

It's super handy to make RSC streamable primitives chainable to create values inline. For example, unify type definitions with inline streamable values:

if (loggedIn) {
  const userCard = createStreamableUI()

  // LLM logic to update `userCard`...

  return {
    display: userCard.value
  }
} else {
  return {
    display: createStreamableUI().done(<div>Please login</div>).value
  }
}

[JClackett]

has this been released? it seems to work but the types say I cant chain yet?

[unstubbable]

We might need explicit type annotations here, since tsup is now inferring any as return type for update/append/error/done. This is also the case with the experimentalDts option.