Function every_level_alive 

pub fn every_level_alive() -> bool

phase-509 P7 (RFC-0108 D8) – which level an executor is, and whether every level of the image is alive: what a supervisor that owns a route per level or feeds a watchdog reads, and what a board’s tier runner states (the level count, and each tier’s level by tier_level_by). Plain atomics in nros-node, so ungated. Whether every level of the image has checked in since the last take_every_level_alive that returned true.