Function app_is_active 

pub(crate) fn app_is_active(last_used_time_stop: Option<u64>) -> bool

The Windows webcam-in-use rule: an app’s LastUsedTimeStop of 0 means it is currently streaming (a non-zero value is the timestamp it stopped). Extracted so the rule itself is testable without a registry; the registry walk in windows::any_active_app feeds it. Un-gated so it’s tested everywhere; only the Windows walk calls it in non-test builds.