feat: Add #[Computed] attribute for virtual model properties

[techmahedy]

What

Introduces #[Computed] — a method-level attribute that marks a model method as a virtual property. Computed properties are derived values that are never persisted to the database but are automatically included in toArray() and json_encode() output.

Why

Previously, virtual properties had to be appended manually or handled outside the model. There was no first-class way to declare derived attributes that serialize cleanly alongside real database columns.

How it works

class User extends Model
{
    #[Computed]
    public function fullName(): string
    {
        return $this->name . ' ' . $this->email;
    }
}

// Both access styles work
$user->full_name   // "John Doe"  ← snake_case
$user->fullName    // "John Doe"  ← camelCase works too

// toArray() / json_encode() always uses snake_case
$user->toArray();
// ['name' => '...', 'email' => '...', 'full_name' => 'John Doe']

// makeHidden respects both names
$user->makeHidden(['full_name'])->toArray();
$user->makeHidden(['fullName'])->toArray();  // either works

Behaviour

• Method name is automatically converted to snake_case as the serialization key
• Accessible via both $model->full_name and $model->fullName
• Included in toArray() and json_encode() automatically
• Never written to the database — invisible to dirty checking and save()
• Supports makeHidden() by either the snake_case key or the method name
• Reflection runs once per class and is statically cached

Files

• Database/Entity/Attributes/Computed.php — new attribute
• Database/Entity/Computed/InteractsWithComputedProperties.php — new trait
• Database/Entity/Model.php — added trait, updated __get() and makeVisible()