Description:
------------
Right now, the unserialize callback must be defined using an ini setting.
It would be more convenient to be able to set it via new option.
(This could potentially also allow setting it to a Closure?)

BEFORE:
$unserializeCallbackHandler = ini_set('unserialize_callback_func', 'my_unserialize_callback');
try {
    unserialize($value);
} finally {
    ini_set('unserialize_callback_func', $unserializeCallbackHandler);
}

AFTER:
unserialize($value, ['callback' => 'my_unserialize_callback']);