import { PartialReader } from "https://deno.land/x/stream_slicing@v1.1.0/partial_reader.ts";
Returns a ReadableStream that the underlying reader is redirected to for the
next size bytes.
If you want to assert that the returned stream outputs size bytes without ending early,
then use .pipeThrough(new ExactBytesTransformStream(size)) on the result.