Restore access to request extensions in guards

Restore access to request extensions in guards: a task in LegoFlow-SWE (Harbor dataset). After recent internal changes, guards implementing the Guard trait lost the ability to access request extensions. The Guard::check method currently receives only a &RequestHead , which no longer provides a…

The task

After recent internal changes, guards implementing the `Guard` trait lost the ability to access request extensions. The `Guard::check` method currently receives only a `&RequestHead`, which no longer provides a direct path to extensions. Previously, guards could reach extensions through the head, enabling patterns…

Part of Lego-X/LegoFlow-SWE.