PHPUnit 10 Migration (#1302)

* Bump PHPUnit dependencies

* Set return type of base TestCase methods

From the [PHPUnit 8 release notes][1], the `TestCase` methods below now declare a `void` return type:

- `setUpBeforeClass()`
- `setUp()`
- `assertPreConditions()`
- `assertPostConditions()`
- `tearDown()`
- `tearDownAfterClass()`
- `onNotSuccessfulTest()`

[1]: https://phpunit.de/announcements/phpunit-8.html

* Ignore PHPUnit cache folder

* Adopt PHP attributes in test classes

* Declare data providers as `static`

* Add return types to test methods

* Define test classes as `final`

* Migrate phpunit.xml to phpunit 10

* Correct phpunit attribute class name

* Rename base test class

* Restructure test folders

* Fix test image paths

* Only set rules for php files in .editorconfig

* Remove php unit flag in local test env

---------

Co-authored-by: Shift <shift@laravelshift.com>

tests/Unit/Geometry/Factories/RectangleFactoryTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Intervention\Image\Tests\Unit\Geometry\Factories;
+
+use Intervention\Image\Geometry\Factories\RectangleFactory;
+use Intervention\Image\Geometry\Point;
+use Intervention\Image\Geometry\Rectangle;
+use Intervention\Image\Tests\BaseTestCase;
+
+final class RectangleFactoryTest extends BaseTestCase
+{
+    public function testFactoryCallback(): void
+    {
+        $factory = new RectangleFactory(new Point(1, 2), function ($rectangle) {
+            $rectangle->background('fff');
+            $rectangle->border('ccc', 10);
+            $rectangle->width(100);
+            $rectangle->height(200);
+            $rectangle->size(1000, 2000);
+        });
+
+        $rectangle = $factory();
+        $this->assertInstanceOf(Rectangle::class, $rectangle);
+        $this->assertTrue($rectangle->hasBackgroundColor());
+        $this->assertEquals('fff', $rectangle->backgroundColor());
+        $this->assertEquals('ccc', $rectangle->borderColor());
+        $this->assertEquals(10, $rectangle->borderSize());
+        $this->assertEquals(1000, $rectangle->width());
+        $this->assertEquals(2000, $rectangle->height());
+    }
+}