feat: move Expectations API out of external plugin

tests/Features/Expect/toBeGreatherThan.php

@@ -0,0 +1,16 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('passes', function () {
+    expect(42)->toBeGreaterThan(41);
+    expect(4)->toBeGreaterThan(3.9);
+});
+
+test('failures', function () {
+    expect(4)->toBeGreaterThan(4);
+})->throws(ExpectationFailedException::class);
+
+test('not failures', function () {
+    expect(5)->not->toBeGreaterThan(4);
+})->throws(ExpectationFailedException::class);