SoloDeadlineDetector

the smallest membership that counts as paired, including this peer. 2 means "never paired with anyone". Must be at least 2.

how long to wait for that membership. Must be positive.

supplies the SoloDeadlineEvent.at timestamps; injected so tests can fix it — never Clock.System reached for directly.

the scope the deadline timer runs on. Required: a default real dispatcher would silently decouple the timer from a test's virtual clock.