feat: add content package schema validator

src/Package/PackageValidationResult.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Package validation result.
+ *
+ * @package WPContentSync
+ */
+
+namespace WPContentSync\Package;
+
+final class PackageValidationResult {
+	/** @var array<int, string> */
+	private array $errors;
+
+	/**
+	 * @param array<int, string> $errors Validation errors.
+	 */
+	private function __construct( array $errors ) {
+		$this->errors = array_values( $errors );
+	}
+
+	public static function valid(): self {
+		return new self( array() );
+	}
+
+	/**
+	 * @param array<int, string> $errors Validation errors.
+	 */
+	public static function invalid( array $errors ): self {
+		return new self( $errors );
+	}
+
+	public function isValid(): bool {
+		return array() === $this->errors;
+	}
+
+	/**
+	 * @return array<int, string>
+	 */
+	public function errors(): array {
+		return $this->errors;
+	}
+}