Feature: Add deferred resolution to model factory

[kjohnson]

Related impress-org/givewp#7626

Description

This PR adds deferred resolution to model factory definitions, such as nested model factories, so that defaults can be overridden without instantiating unused model instances.

Affects

Updates src\Models\Factories\ModelFactory::makeInstance() to support resolving attributes that are callable.

Visuals

public function definition(): array
{
    return [
        'title' => __('GiveWP Campaign', 'give'),
        'formId' => DonationForm::factory()->createAndResolveTo('id'),
    ];
}

[JasonTheAdams]

Thank you for porting this over, @kjohnson! 💪

I would like @borkweb to approve this as well, as I've already seen this and would like his thoughts if he has any. 😄

[borkweb]

This looks great! I added a small commit with some standards changes to formatting, but otherwise this is 👨‍🍳 💋

I went ahead and updated @unreleased to @since 1.2.3. You can merge this and tag the release 🕺

[kjohnson]

@borkweb @JasonTheAdams what is the procedure for merging PR for this repo? The PR is approved - can it be merged?

[JasonTheAdams]

Thank you for following up on this, @kjohnson! It's a really handy feature and we appreciate your efforts!

[JasonTheAdams]

Just released this in 1.2.3: https://github.com/stellarwp/models/releases/tag/1.2.3 🎉