Time only close() in WasUpAllAlong drain test

testAsyncCloseDrainSucceedsWhenServerWasUpAllAlong timed the whole
try (Sender = fromConfig(...)) { write; flush; } close block against a
2500ms budget, but the assertion budgets close()'s drain latency, not
sender construction. Iteration 0 is the first store-and-forward async
sender in the JVM, so fromConfig pays a one-time cold-start cost (class
loading, JIT, sf buffer mmap). On a loaded CI runner that cold start
reached ~3.26s and tripped the assertion, even though close() itself
took ~12ms.

Move t0 to wrap only sender.close(), matching the sibling test
testAsyncCloseDrainSucceedsWhenServerStartsDuringDrain. close() is
idempotent, so the try-with-resources auto-close is a no-op. Measured
close() latency stays in the single-digit milliseconds across all 20
iterations, well within the 2500ms budget.

Author: mtopolnik

core/src/test/java/io/questdb/client/test/cutlass/qwp/client/CloseDrainTest.java

@@ -358,14 +358,20 @@ public void testAsyncCloseDrainSucceedsWhenServerWasUpAllAlong() throws Exceptio
                         + ";reconnect_initial_backoff_millis=20"
                         + ";reconnect_max_backoff_millis=100"
                         + ";close_flush_timeout_millis=3000;";
-                long t0 = System.nanoTime();
                 try (Sender sender = Sender.fromConfig(cfg)) {
                     sender.table("foo").longColumn("v", i).atNow();
                     sender.flush();
+                    // Time only close(): the 2500ms budget covers close()'s
+                    // drain latency. Building the first store-and-forward
+                    // sender carries a one-time cold-start cost (class
+                    // loading, JIT, sf buffer mmap) that belongs to
+                    // construction, not to close().
+                    long t0 = System.nanoTime();
+                    sender.close();
+                    long elapsedMs = (System.nanoTime() - t0) / 1_000_000;
+                    Assert.assertTrue("iteration " + i + " close() took " + elapsedMs + "ms",
+                            elapsedMs < 2500);
                 }
-                long elapsedMs = (System.nanoTime() - t0) / 1_000_000;
-                Assert.assertTrue("iteration " + i + " close() took " + elapsedMs + "ms",
-                        elapsedMs < 2500);
             }
         }
     }