[9.x] Pass thrown exception to $sleepMilliseconds closure in retry helper

[arondeparon]

What does this pull request implement?

This pull requests implement a backwards-compatible change to the retry helper. The retry helper accepts either an int or a Closure. When passing a Closure object, the $attempts parameter would be passed, allowed users to implement their own backoff algorithm.

In some cases, however, it would be desirable to implement a backoff strategy based on the exception that was thrown, for example in the case of an API client that returns a specific exception in the case of a HTTP 429. In such cases, the exception thrown could potentially hold information as to how long a user has to wait before a new attempt will be excepted.

This pull request allows you to access the thrown exception instance in the $sleepMilliseconds closure to implement a dynamic backoff strategy.

Example use case

Imagine an API library that throws the following exception in the case of a HTTP 429:

<?php

class TooManyRequestsException extends ApiException
{
    public int $retryAfterNumberOfSeconds;

    public int $currentRateLimit;

    public int $rateLimitResetsAfterTimestamp;
}

Using the above information, we would be able to implement a dynamic backoff strategy as follows:

retry(3, function() {
    // Perform some kind of external API call
}, function($attempts, $exception) {
    // Use the information provided by the external API to provide `rescue` with a dynamic delay
    return $exception->retryAfterNumberOfSeconds / 1000;
});