feat: add asyncComputed, asyncEffect

[johnsoncodehk]

Add asyncComputed, asyncEffect APIs, which is based on comma operator and function* design implementation.

Example:

const src = signal('fallback data');

const asyncComp = asyncComputed(async function* () {
  const data = await fetchSomeData();
  if (data) {
    return data;
  }
  const fallbackData = (yield src, src).get();
  return fallbackData;
});

asyncEffect(async function* () {
  const data = await (yield asyncComp, asyncComp).get();
  console.log('Effect triggered with value:', value);
});

src.set(2);

[johnsoncodehk]

This API was added for my personal needs (I will use it in https://github.com/volarjs/volar.js), and its usage will probably not meet most people's expectations. Therefore this feature will be unstable and it is not recommended to use.