Rename namespace Aternos\Codex to IndifferentKetchup\Codex

Bulk substitution across all PHP files in src/ and test/. Covers
namespace declarations, use statements, fully-qualified class
references, and @package PHPDoc tags. No logic changes.

src/Log/LevelInterface.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace Aternos\Codex\Log;
+namespace IndifferentKetchup\Codex\Log;
 
 use JsonSerializable;