Placeholder AlarmStateChanged rows are a DebugView snapshot-only concept emitted
by InstanceActor.BuildAlarmStatesSnapshot; they are never a real alarm transition.
Their timestamp may be DateTimeOffset.MinValue (the Protobuf Timestamp lower boundary),
which can throw when packed via Timestamp.FromDateTimeOffset.
Added early-return guard at the top of HandleAlarmStateChanged before any timestamp
pack or channel write. Updated the existing NativeBindingLinkage round-trip test to
use a real (non-placeholder) native alarm; added DropsAlarmStateChanged_WhenIsConfiguredPlaceholder
to assert placeholders are silently dropped (15/15 pass).
Joseph Doherty
e7660134f2