This PR renames containsOneItem() to hasSole(), and adds callback and operator support.

Background

Back in #36428, I added an isSingle() method to check if a collection contains exactly one item. Taylor later renamed it to containsOneItem() because—and I quote—"it's not a dating app" 😄

The problem is that containsOneItem() is actually longer than count() === 1, making the method rather pointless.

New Method

Now that we have the sole() nomenclature, we can add a hasSole() method that...

• Is shorter and more expressive than containsOneItem()
• Supports the same filter signatures as sole() (callback, key/value, and full operator syntax)

$collection->hasSole();
$collection->hasSole(fn ($item) => $item->active);
$collection->hasSole('status', 'pending');
$collection->hasSole('age', '>=', 21);

Deprecation

containsOneItem() is now deprecated and delegates to hasSole().

Laravel 13

After this is merged, and then merged into master, we'll add this method to the Enumerable interface, and remove the containsOneItem() method completely.