Add support for AbortSignal to all API methods

[aron]

This PR adds support for passing AbortSignal to all API methods that make HTTP requests, these are passed directly into the native fetch() implementation, so it's up to the user to handle the AbortError raised, if any.

const controller = new AbortController();
try {
  const prediction = await replicate.predictions.create({
    version: 'xyz',
    ...,
    signal: controller.signal,
  });
} catch (err) {
  if (err instanceof DOMException && err.name === "AbortError") {
    ...
  }
}

The paginate function also checks to see whether the signal was aborted before proceeding to the next iteration. If so it returns immediately to avoid making a redundant fetch call.

This allows the client to take advantage of various frameworks that provide an AbortSignal instance to tear down any in flight requests.

[erbridge]

One minor comment about the docs, but otherwise, I think this looks good.