[11.x] Add throttle method to LazyCollection

[JosephSilber]

Allows throttling the values retrieved from a lazy collection:

LazyCollection::times(3)->throttle(seconds: 1)->each(function ($number) {
    dump($number); // Will dump each number, with a pause (sleep) of about a second in between each...
});

Note: The sleep will not be 1 second. That would be quite naïve. Instead, it includes the time it takes to process each retrieved value, and only sleeps for the remainder of the duration.

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Especially useful when interacting with external APIs, which may have some rate limits. Can be used both for pulling data as well as for pushing data.

Pulling data example:

$userIds = collect([1, 2, 3])->lazy();

$users = $userIds
    ->throttle(1)
    ->map(fn ($userId) => API::fetchUser($id));

Or, if the external API supports fetching, say, 50 users at once:

$userIds = collect([1, 2, 3, /* ... */])->lazy();

$users = $userIds
    ->chunk(50)
    ->throttle(1)
    ->map(fn ($userIds) => API::fetchUsers($userIds))
    ->flatten();

Pushing data example:

$userIds = collect([1, 2, 3])->lazy();

$userIds
    ->throttle(1)
    ->each(fn ($userId) => API::deleteUser($id));

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Here's a real-world use case, which would be vastly simplified after this PR:

DB::table('stock_sync')->cursor()->throttle(1)->map(function ($sync) {
    // Handle stock sync updates...
});

[timacdonald]

This is pretty sick.