Spec §9 decision J: an estimate outside the plausibility bounds doesn't
count. A max-based peer_time_estimate always returned a forged
observed_at = u64::MAX, which the host then rejected, so it never saw
the honest estimates and stayed quarantined.
LogStoreBuilder::plausible_wall_ms(floor..=ceiling) sets the range
(default unbounded, so behaviour is unchanged when unset), and
peer_time_estimate filters candidates against it before taking the
max. The WallClockStore signature is unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>