fix: exit() and dd() support in worker mode (#1946)

* Verifies exit behavior.

* formatting

* Checks for actual exit.

* Fixes test.

* Fixes test.

* Update testdata/dd.php

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

---------

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

testdata/dd.php

@@ -0,0 +1,32 @@
+<?php
+
+// simulate Symfony's dd() behavior
+// see https://github.com/symfony/http-kernel/blob/7.3/DataCollector/DumpDataCollector.php#L216
+class Dumper
+{
+    private string $message;
+
+    public function dump(string $message): void
+    {
+        http_response_code(500);
+        $this->message = $message;
+    }
+
+    public function __destruct()
+    {
+        if (isset($this->message)) {
+            echo $this->message;
+        }
+    }
+}
+
+$dumper = new Dumper();
+
+while (frankenphp_handle_request(function () use ($dumper) {
+    $dumper->dump($_GET['output'] ?? '');
+    exit(1);
+})) {
+    // keep handling requests
+}
+
+echo "we should never reach here\n";