feat: move Expectations API out of external plugin

tests/Features/Expect/toBeFloat.php

@@ -0,0 +1,16 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('pass', function () {
+    expect(1.0)->toBeFloat();
+    expect(1)->not->toBeFloat();
+});
+
+test('failures', function () {
+    expect(42)->toBeFloat();
+})->throws(ExpectationFailedException::class);
+
+test('not failures', function () {
+    expect(log(3))->not->toBeFloat();
+})->throws(ExpectationFailedException::class);