Struct worker::crypto::DigestStreamCopy item path

let digest_stream = DigestStream::new(DigestStreamAlgorithm::Sha256);

// create a ReadableStream from a string
let mut req_init = web_sys::RequestInit::new();
req_init.method("POST");
req_init.body(Some(&JsValue::from_str("foo")));
let req = web_sys::Request::new_with_str_and_init("http://internal", &req_init).unwrap();
let body = req.body().unwrap();

// just kick the promise off to the background, we'll await the digest itself
// since this is piped to a JS readable stream, call .raw() to get the underlying JS object
let _ = body.pipe_to(digest_stream.raw());

let bytes:Vec<u8> = digest_stream.digest().await.unwrap().to_vec();