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/src/log_test.dart

@@ -46,7 +46,7 @@ void main() {
       final sub = log.records.listen(out.add);
       log.info('s', 'm1');
       log.info('s', 'm2');
-      await Future<void>.delayed(Duration.zero);
+      await pumpEventQueue();
       expect(out.map((r) => r.message), ['m1', 'm2']);
       await sub.cancel();
       await log.dispose();