Change default executor service implementation to WORKER_THREAD_POOL

[marcphilipp]

Resolves #5291.

[testlens-app]

✅ All tests passed ✅

⚠️ TestLens detected flakiness ⚠️

Test Summary

CI / Build / Windows > :jupiter-tests:test

Test	Runs	Flakiness
@Timeout > separate thread > when one test is stuck "forever" the next tests should not get stuck	⚠️	1% 🟡

🏷️ Commit: b3eb839
▶️ Tests: 29725 executed
⚪️ Checks: 16/16 completed

Test Failures

@Timeout > separate thread > when one test is stuck "forever" the next tests should not get stuck (:jupiter-tests:test in CI / Build / Windows)

org.opentest4j.AssertionFailedError: 
expected: SUCCESSFUL
 but was: FAILED
	at org.junit.jupiter.engine.extension.TimeoutExtensionTests$SeparateThread.oneThreadStuckForever(TimeoutExtensionTests.java:426)

expected	actual
SUCCESSFUL	FAILED

---

Learn more about TestLens at testlens.app/docs.