[NFR]: Extract a neutral injection method from ResponseListener #39

Summary

The injection logic can run only through an event call. A host with no events manager cannot inject the bar. Move the logic to a public method that takes only a response.

Current state

• ResponseListener::__invoke(EventInterface $event, mixed $source, mixed $response) holds all the logic (src/DebugBar/ResponseListener.php:55).
• The logic does not use $event or $source.
• Injector is already neutral and does not change.

Proposed direction

• Add a public method that takes a Phalcon\Http\ResponseInterface, and move the logic to it.
• __invoke() keeps the instanceof check and calls the new method.

Acceptance

• A test calls the new method with no event, and the bar is injected.
• The existing ResponseListenerTest tests pass with the same expected results.
• Tests pass with full coverage. phpcs and phpstan pass.

Part of

#13