feat: initiate retry on failure.

[jiangtao-zzz]

for example, when a slice fails to upload a large file, you need to try again.

Fixes #25

[rxaviers]

Thank you very much for the details in #25 and for this PR, now the point is clear to me. cc @JiangTaoZzzz

Instead of implementing the retry mechanism in this library/fn, would it be possible to do it in the user code itself? This way we keep this library/fn simple and we are still able to fulfill such usecase. For example:

async function mySuperUpload(...args) {
  if (!await uploadAndRetryACoupleOfTimesBeforeItFails(...args)) {
    throw new Error("...");
  }
  return ...;
}

await asyncPool(2, [dataSlice1, dataSlice2, ...], mySuperUpload);

[jiangtao-zzz]

Oh, that's true. Your idea is better. Thank you very much, I got.

[rxaviers]

You're very welcome. I am going to close the PR and the linked issue. If there are any other points / use cases that can't be done this way, let me know. We can reconsider it.