test(aot): 添加空类型属性测试用例

- 添加了具有可空字符串类型的属性测试
- 实现了包含状态码短语常量的响应类
- 添加了获取原因方法的测试逻辑
- 验证了空合并操作符的功能
- 测试了不同状态码下的返回值情况

tests/aot/prop-002.phpt

@@ -0,0 +1,40 @@
+--TEST--
+Property with nullable type
+--FILE--
+<?php
+class Response
+{
+    public ?string $reason;
+
+    public const PHRASES = [
+        100 => 'Continue',
+        101 => 'Switching Protocols',
+        102 => 'Processing', // WebDAV; RFC 2518
+        103 => 'Early Hints', // RFC 8297
+    ];
+
+    public function __construct() {
+
+    }
+
+    public function getReason(int $status): string
+    {
+        $reason = $this->reason ?: self::PHRASES[$status] ?? 'unknown';
+        return $reason;
+    }
+}
+
+function main() {
+    $resp = new Response;
+    var_dump($resp->getReason(102));
+    var_dump($resp->getReason(200));
+    $resp->reason = 'OK';
+    var_dump($resp->getReason(102));
+    var_dump($resp->getReason(200));
+}
+?>
+--EXPECT--
+string(10) "Processing"
+string(7) "unknown"
+string(2) "OK"
+string(2) "OK"