declarativeNetRequest.getSessionRules reports that rule exists before it's active

`declarativeNetRequest.getSessionRules()` reports that session rules exist before they are actually active.

Our extension blocks social media widgets with DNR rules and replaces them with click-to-activate placeholders.
When a user clicks to activate a widget, we add a session rule to allow the social media request and wait for getSessionRules to confirm its presence before reloading the widget. Even after getSessionRules reports that the allow rule exists, the request is blocked for several seconds (2-8). This breaks our widget activation functionality which relies on getSessionRules to accurately report active session rules. This is not a problem on Chrome.

This delay does not occur in a demo extension with just a few rules, but does affect the Privacy Badger prototype which has around 4,000 dynamic rules and 20 session rules.

Expected Behavior: When getSessionRules reports that a session rule exists, it should be active.

Apple Feedback Assistant Report: [FB16491079](https://feedbackassistant.apple.com/feedback/16491079)