fix(php): 修复原生类型变量和对象属性的 unset 操作问题

- 修改对象属性 unset 警告消息为更准确的描述
- 添加对原生类型变量的 unset 操作检查和警告
- 阻止原生类型变量执行 unset 操作
- 新增 unset 原生类型变量的测试用例
- 完善变量类型检查逻辑以区分原生类型

examples/error/unset-int-var.php

@@ -0,0 +1,9 @@
+<?php
+use native_types;
+
+function main()
+{
+    $x = 100;
+    unset($x);
+    var_dump($x);
+}

src/Php/CompilerBase.php

@@ -3432,7 +3432,7 @@ class CompilerBase extends \PhpAot\Core\Translator
                 if ($object === 'this_' and $this->isIdExpr($var->name)) {
                     $propName = $this->parseIdentifier($var->name);
                     if ($this->hasObjectPropVar($this->getObjectPropVarName($object, $propName))) {
-                        $this->warning($var, "Unset of object property `{$propName}` is not allowed");
+                        $this->warning($var, "Object property `$propName` of native types cannot be unset");
                         $lines = [];
                         $lines[] = $this->getObjectPropVarName($object, $propName) . " = 0;";
                     }
@@ -3442,7 +3442,12 @@ class CompilerBase extends \PhpAot\Core\Translator
                 if (!$this->hasVar($name)) {
                     $this->errorUndefinedVariable($var);
                 }
-                $lines[] = "{$name}.unset();";
+                $type = $this->getVarType($name);
+                if ($this->isNativeType($type)) {
+                    $this->warning($var, "Variable of native type `\${$name}` cannot be unset");
+                } else {
+                    $lines[] = "{$name}.unset();";
+                }
             } else {
                 $this->fatalError($var, "Unsupported unset type `{$var->getType()}`");
             }