feat: DTO에 DefaultValue, DefaultValueGenerator 추가

src/sammo/DTO/Attr/DefaultValue.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace sammo\DTO\Attr;
+
+#[\Attribute(\Attribute::TARGET_PROPERTY)]
+class DefaultValue
+{
+  public function __construct(public readonly null|bool|int|float|string|array $defaultValue)
+  {
+  }
+
+  public function getDefaultValue(): mixed
+  {
+    return $this->defaultValue;
+  }
+}

src/sammo/DTO/Attr/DefaultValueGenerator.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace sammo\DTO\Attr;
+
+#[\Attribute(\Attribute::TARGET_PROPERTY)]
+class DefaultValueGenerator
+{
+  public function __construct(public readonly string $generator)
+  {
+    if (!is_callable($generator)) {
+      throw new \Exception("$generator is not a callable");
+    }
+  }
+
+  public function getDefaultValue(): mixed
+  {
+    $generator = $this->generator;
+    return $generator();
+  }
+}