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/ModifierStackTest.php

@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Intervention\Image\Tests\Unit;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use Intervention\Image\Modifiers\GreyscaleModifier;
+use Intervention\Image\Interfaces\ImageInterface;
+use Intervention\Image\Interfaces\ModifierInterface;
+use Intervention\Image\ModifierStack;
+use Intervention\Image\Tests\BaseTestCase;
+use Mockery;
+
+#[CoversClass(\Intervention\Image\ModifierStack::class)]
+final class ModifierStackTest extends BaseTestCase
+{
+    public function testConstructor(): void
+    {
+        $stack = new ModifierStack([]);
+        $this->assertInstanceOf(ModifierStack::class, $stack);
+    }
+
+    public function testPush(): void
+    {
+        $stack = new ModifierStack([]);
+        $result = $stack->push(new GreyscaleModifier());
+        $this->assertInstanceOf(ModifierStack::class, $result);
+    }
+
+    public function testApply(): void
+    {
+        $image = Mockery::mock(ImageInterface::class);
+
+        $modifier1 = Mockery::mock(ModifierInterface::class)->makePartial();
+        $modifier1->shouldReceive('apply')->once()->with($image);
+
+        $modifier2 = Mockery::mock(ModifierInterface::class)->makePartial();
+        $modifier2->shouldReceive('apply')->once()->with($image);
+
+        $stack = new ModifierStack([$modifier1, $modifier2]);
+        $result = $stack->apply($image);
+        $this->assertInstanceOf(ImageInterface::class, $result);
+    }
+}