Add POC test exposing bug in Timeouts.shutdown() implementation

Demonstrates that calling Timeouts.shutdown() (as GenericContainer.stop()
does in this PR) permanently kills the static shared ExecutorService,
causing all subsequent Timeouts usage to fail with
RejectedExecutionException. This breaks any test suite that stops one
container and then starts another.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

core/src/test/java/org/testcontainers/utility/TimeoutsShutdownTest.java

@@ -0,0 +1,35 @@
+package org.testcontainers.utility;
+
+import org.junit.Test;
+import org.testcontainers.utility.ducttape.Timeouts;
+
+import java.util.concurrent.TimeUnit;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Verifies that {@link Timeouts} works correctly across shutdown/reuse cycles.
+ * After {@code shutdown()} the executor is re-created on next use.
+ */
+public class TimeoutsShutdownTest {
+
+    @Test
+    public void timeoutsWorkAfterShutdown() {
+        // First use
+        String result1 = Timeouts.getWithTimeout(5, TimeUnit.SECONDS, () -> "container-1-ready");
+        assertThat(result1).isEqualTo("container-1-ready");
+
+        // Shutdown (as GenericContainer.stop() does)
+        Timeouts.shutdown();
+
+        // Second use — should transparently create a fresh executor
+        String result2 = Timeouts.getWithTimeout(5, TimeUnit.SECONDS, () -> "container-2-ready");
+        assertThat(result2).isEqualTo("container-2-ready");
+
+        // Shutdown and use again to confirm repeatable
+        Timeouts.shutdown();
+
+        String result3 = Timeouts.getWithTimeout(5, TimeUnit.SECONDS, () -> "container-3-ready");
+        assertThat(result3).isEqualTo("container-3-ready");
+    }
+}