Add extension version and env check method (#458)

src/SPC/builder/extension/protobuf.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SPC\builder\extension;
+
+use SPC\builder\Extension;
+use SPC\util\CustomExt;
+
+#[CustomExt('protobuf')]
+class protobuf extends Extension
+{
+    public function validate(): void
+    {
+        if ($this->builder->getPHPVersionID() < 80000 && getenv('SPC_SKIP_PHP_VERSION_CHECK') !== 'yes') {
+            throw new \RuntimeException('The latest protobuf extension requires PHP 8.0 or later');
+        }
+    }
+}