Stabilize JDK 21 flaky assertion in DelegatingScheduledExecutorServiceTest

[Copilot]

build (21) was failing due to a nondeterministic assertion in DelegatingScheduledExecutorServiceTest: shutdownNow() occasionally returned an empty list under JDK 21 scheduling timing. This change makes the test deterministic by guaranteeing a pending task exists at shutdown.

• Root cause addressed

  • assertFalse(instance.shutdownNow().isEmpty()) depended on transient queue state and could fail when no pending tasks remained.

• Test hardening change

  • Added a long-delay scheduled task immediately before shutdownNow() so the executor always has at least one queued, non-started task.
  • Added TimeUnit.DAYS static import for the long-delay scheduling call.

• Relevant code change

  instance.schedule(() -> {
      log("delayed schedule");
  }, 1, DAYS);
  
  assertFalse(instance.shutdownNow().isEmpty());

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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