fix: wrap bare intersection types in parentheses when adding nullable (#1756)

When a MorphTo relation's docblock uses a bare intersection type in the
generic parameter (e.g. `MorphTo<BaseModel&CanBeAssigned, $this>`), the
generated property type incorrectly becomes `BaseModel&CanBeAssigned|null`
instead of the correct `(BaseModel&CanBeAssigned)|null`.

This adds `wrapIntersectionType()` which ensures bare intersection types
are wrapped in parentheses before `|null` is appended, producing valid
DNF type syntax. Applied in both `setProperty()` and `applyNullability()`.

tests/Console/ModelsCommand/MorphToIntersection/Models/CanBeAssigned.php

@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Barryvdh\LaravelIdeHelper\Tests\Console\ModelsCommand\MorphToIntersection\Models;
+
+interface CanBeAssigned
+{
+}