test: poll for port release in TcpServerTest to fix flake

After TcpServer.close(), there can be a brief OS-level delay before
the port is fully released. Replace the immediate assertion with a
polling helper that retries for up to 1 second.

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

Author: devin-ai-integration[bot]

lib/shared/test-helpers/src/test/java/com/launchdarkly/testhelpers/tcptest/TcpServerTest.java

@@ -21,7 +21,7 @@ public void listensOnAnyAvailablePort() throws IOException {
       port = server.getPort();
       try (Socket s = new Socket("localhost", server.getPort())) {} // just verify that we can connect
     }
-    assertFalse("expected listener to be closed, but it wasn't", doesPortHaveListener(port));
+    assertPortReleased(port);
   }
 
   @Test
@@ -37,6 +37,21 @@ public void listensOnSpecificPort() throws IOException {
       assertEquals(specificPort, server.getPort());
       try (Socket s = new Socket("localhost", specificPort)) {} // just verify that we can connect
     }
-    assertFalse("expected listener to be closed, but it wasn't", doesPortHaveListener(specificPort));
+    assertPortReleased(specificPort);
+  }
+
+  private static void assertPortReleased(int port) {
+    long deadline = System.currentTimeMillis() + 1000;
+    while (System.currentTimeMillis() < deadline) {
+      if (!doesPortHaveListener(port)) {
+        return;
+      }
+      try {
+        Thread.sleep(50);
+      } catch (InterruptedException e) {
+        throw new RuntimeException(e);
+      }
+    }
+    assertFalse("expected listener to be closed, but it wasn't", doesPortHaveListener(port));
   }
 }