fix fallbackAsync for async arg & add relevant tests

[EltonLobo07]

This PR fixes the issue related to fallbackAsync given any async schema.

Issue:

When the validation of an async schema fails, fallbackAsync still returns the default value instead of the supplied fallback value. The code block given below exposes this bug.

import * as v from 'valibot';

const Schema = v.fallbackAsync(
  v.pipeAsync(
    v.string(),
    v.checkAsync(async (value) => false)
  ),
  "fallback"
);

// logs: default
console.log(await v.safeParseAsync(Schema, "default"));

Fix:

Inside the _run method of the object returned by fallbackAsync, wait for the schema to run completely before checking if the dataset has any issues. This is needed as fallbackAsync can be given an async schema that might execute some async code.

Additional information:

Simply waiting for the async code to complete fixes the issue, but I was worried about the rejected promise case. I checked some of the other methods and found out that there is no logic to catch rejected promises. I assume this is intentional, and the thought process behind this approach would be to let the user handle rejected promises. Let me know if my assumption is incorrect.

[fabian-hiller]

Thanks for this fix! Yes, at the moment we expect the user to catch async errors.

[fabian-hiller]

v0.37.0 is available