Integrate pest-plugins with 2 interfaces

integrate pest-plugin package and remove core coverage stuff

src/Contracts/Plugins/AddsOutput.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Contracts\Plugins;
+
+use Pest\TestSuite;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * @internal
+ */
+interface AddsOutput
+{
+    /**
+     * Allows to add custom output after the test suite was executed.
+     */
+    public function addOutput(TestSuite $testSuite, OutputInterface $output, int $testReturnCode): void;
+}