feat: add a woker mode (#1)

* refactor: better memory management

* wip

* tmp

* introduce a go-like api

* upgraded to PHP 8.2

* Fix thread safety issues

* fix tests

* wip

* refactor worker

* worker prototype

* fix populate env

* session

* improve tests

* fix Caddy tests

* refactor

testdata/_executor.php

@@ -0,0 +1,9 @@
+<?php
+
+$fn = require $_SERVER['SCRIPT_FILENAME'];
+if (!isset($_SERVER['FRANKENPHP_WORKER'])) {
+    $fn();
+    return;
+}
+
+while (frankenphp_handle_request($fn)) {}