Add custom package downloader and extractor

src/SPC/store/pkg/CustomPackage.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SPC\store\pkg;
+
+abstract class CustomPackage
+{
+    abstract public function getSupportName(): array;
+
+    abstract public function fetch(string $name, bool $force = false, ?array $config = null): void;
+
+    public function extract(string $name): void
+    {
+        throw new \RuntimeException("Extract method not implemented for package: {$name}");
+    }
+}