Allow custom arch expectations

Author: olivernybroe

src/Expectation.php

@@ -330,7 +330,7 @@ public function when(callable|bool $condition, callable $callback): self
      * @param  array<int, mixed>  $parameters
      * @return Expectation<TValue>|HigherOrderExpectation<Expectation<TValue>, TValue>
      */
-    public function __call(string $method, array $parameters): Expectation|HigherOrderExpectation|PendingArchExpectation
+    public function __call(string $method, array $parameters): Expectation|HigherOrderExpectation|PendingArchExpectation|ArchExpectation
     {
         if (! self::hasMethod($method)) {
             if (! is_object($this->value) && method_exists(PendingArchExpectation::class, $method)) {
@@ -355,6 +355,10 @@ public function __call(string $method, array $parameters): Expectation|HigherOrd
         $reflectionClosure = new \ReflectionFunction($closure);
         $expectation = $reflectionClosure->getClosureThis();
 
+        if ($reflectionClosure->getReturnType()?->__toString() === ArchExpectation::class) {
+            return $closure(...$parameters);
+        }
+
         assert(is_object($expectation));
 
         ExpectationPipeline::for($closure)