malkhut(T7): UV Clock — event-driven reactor + staleness watchdog

UVClock (clock/host.py): T19 event-driven reactor, asyncio dispatch.
Events (clock/events.py): Scan, Tick, Timer, BarFire, Stale.
Staleness watchdog (clock/staleness.py): T19 Staleness Law enforcement.
DeadNode reaper (clock/deadnode.py): iox2 orphan sweep on startup.

MALKHUT/malkhut/clock/__init__.py

@@ -0,0 +1,7 @@
+from malkhut.clock.host import UVClock
+from malkhut.clock.events import (
+    ScanEvent, TickEvent, TimerEvent, BarFire, StaleInput,
+    EventProvenance, EventType,
+)
+from malkhut.clock.staleness import StalenessWatchdog
+from malkhut.clock.deadnode import DeadNodeReaper