Fix FakerStubResolver optional() wrapping: nullsafe chain with ?? exa…

[siggi-k]

Fix: optional() wrapping for faker stubs — nullsafe chain + ?? fallback

1. The bug: optional(weight, default)->dateTimeX()->format() fatal error

$faker->optional($weight, $default) is a proxy. On a miss (8 %), it returns $default
as the result of the next proxied method call — without actually calling it.

The previous strategy embedded $example as the default:

// generated (broken):
$faker->optional(0.92, '2020-03-14 21:42:17')->dateTimeThisCentury->format('Y-m-d')

On the 8 % miss, dateTimeThisCentury returns the string '2020-03-14 21:42:17',
then ->format() is called on it → Call to a member function format() on string.

2. The fix: nullsafe chain + ?? $example

optional() without a default returns null on a miss. All subsequent calls are made
nullsafe (?->) so the chain collapses to null, then ?? $example provides the fallback.

Two str_replace passes turn the raw stub into the wrapped form:

1. all -> → ?-> (makes the whole chain nullsafe)
2. $faker?-> → $faker->optional(0.92)-> (restores a normal -> to $faker, inserts optional)

Generated output — before / after:

// datetime column (e.g. updatedAt, nullable, no example in spec):
// before — no wrapping at all (too strict skip condition, see §3):
$model->updatedAt = $faker->dateTimeThisYear('now', 'UTC')->format('Y-m-d H:i:s');

// after:
$model->updatedAt = $faker->optional(0.92)?->dateTimeThisYear('now', 'UTC')?->format('Y-m-d H:i:s') ?? null;

// date column with example:
// before (broken — format() called on string on miss):
$model->archivedAt = $faker->optional(0.92, '2020-03-14')->dateTimeThisCentury->format('Y-m-d');

// after:
$model->archivedAt = $faker->optional(0.92)?->dateTimeThisCentury?->format('Y-m-d') ?? '2020-03-14';

// simple string column with example:
// before:
$model->name = $faker->optional(0.92, 'Acme Corp')->company;

// after:
$model->name = $faker->optional(0.92)?->company ?? 'Acme Corp';

3. Condition for skipping optional wrapping

Before: wrapping was skipped for any field without an example — including nullable ones.
After: wrapping is skipped only when a real value is mandatory:

if (
    (($this->attribute->isRequired() || $this->attribute->nullable === false) && !$this->property->hasAttr('example')) ||
    $this->property->getAttr('uniqueItems')
) {
    return $result; // no optional wrapping
}

Nullable fields without an example now generate null 8 % of the time (semantically correct).
uniqueItems fields are excluded because an optional fallback would break uniqueness.