feat: support network event listening on Page

[AtaLuZiK]

• Add on_request, on_response, on_request_finished, and on_request_failed methods to Page
• Implement event dispatching logic in BrowserContext via dispatch_request_event and dispatch_response_event
• Enhance ResponseObject with status, status_text, and url accessors
• Refactor event subscription in BrowserContext to use Channel::update_subscription
• Add update_subscription helper method to Channel
• Add integration test test_page_support_network_events to verify network event handling

[padamson]

Thanks for this contribution! The implementation follows existing patterns well. A couple of design points to discuss:

Unconditional network event subscriptions

The PR subscribes to request, requestfailed, requestfinished, and response for every BrowserContext, even when no handlers are registered. This adds overhead for all users. Playwright-python handles this lazily, subscribing only when a handler is actually registered. Would you consider deferring subscription to when on_request/on_response/etc. are called? I'm happy to modify before merge if you'd like.

Test event ordering assumption

The test asserts exact event ordering with events.get(0), events.get(1), events.get(2). Since events are dispatched via tokio::spawn, the ordering between request, response, and requestFinished isn't strictly guaranteed. A set-based assertion (or at least a comment explaining why the order is expected to be deterministic) would make this more robust. Again, if you're ok with that, I can make the change before merge.

[AtaLuZiK]

Thank you for the reminder and suggestions! Since I'm just getting started with playwright through my own toy project, I wasn't fully aware of some details. After reviewing the implementation in playwright-dotnet, I agree that subscriptions should be handled lazily. I've spent some time revising the code accordingly.

Regarding the test event ordering, that was an oversight on my part. I don't have a better solution at the moment (perhaps BrowserContext::on_event needs to be async?), so for now I can only sort the actual values before comparing them. I've added comments to explain this situation.