fix: improve file based execution with namespaced PHP snippets

Author: louiswol94

src/php/flat-files/handlers/php-snippet-handler.php

@@ -12,6 +12,7 @@ public function get_dir_name(): string {
 	}
 
 	public function wrap_code( string $code ): string {
-		return "<?php\n\nif ( ! defined( 'ABSPATH' ) ) { return; }\n\n" . $code;
+		$code = "<?php\n\n" . $code;
+		return apply_filters( 'code_snippets_php_snippet_file_code', $code );
 	}
 }