test: deflake the suite — pumpEventQueue instead of Future.delayed(Duration.zero)

~173 `await Future<void>.delayed(Duration.zero)` async-settle waits across 25
test files yield the microtask queue exactly once; when an event→handler chain
needs more than one hop they lose the race under CI's parallel load, so the
failing set varied run to run. Replace with `await pumpEventQueue()` (the
deterministic drain already used elsewhere in the suite); rewired the shared
settle()/tick() helpers in one shot. menu_bar's toggle-close test gets a bounded
extra pump. Verified green under CI=true.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/kernel/log_ring_test.dart

@@ -74,7 +74,7 @@ void main() {
     final sub = ring.changes.listen(events.add);
     ring.add(_rec(LogLevel.info, 'x', 'a'));
     ring.clear();
-    await Future<void>.delayed(Duration.zero);
+    await pumpEventQueue();
     expect(events.length, 2);
     await sub.cancel();
     ring.dispose();
@@ -85,7 +85,7 @@ void main() {
     final events = <void>[];
     final sub = ring.changes.listen(events.add);
     ring.clear();
-    await Future<void>.delayed(Duration.zero);
+    await pumpEventQueue();
     expect(events, isEmpty);
     await sub.cancel();
     ring.dispose();