explore: should CAF support "async generators"? about caf

[getify]

More thoughts:

1. If an async function* does a yield pr instead of await pr, then CAF can cancel immediately and just discard/ignore that yielded promise.

   Of course, await pr in your async function* is kinda the whole point of them... if you didn't want to use await pr, then you could/should just use normal function*. So suggesting this as a "work-around" would kinda just be suggesting an anti-pattern.

2. You don't need to use async function* for emulating cancelable async... that's what function * does. There's no benefit to choosing to use async function* for this synchronous-async pattern. So maybe CAF just doesn't need to support them because it's sorta pointless/moot to support them.

[getify]

I have decided finally... no we won't support async generators. The tipping point is, yield x in an async generator implicitly awaits the value if it's a promise, so... IOW there's no way for CAF to truly stop/finalize an async generator instance with a Promise.race(..) over the yielded value, the way we can do with normal generators.