fix: poll for burst stabilization in MIDI stop test

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

tests/integration.c

@@ -1135,9 +1135,16 @@ static int test_stop_midi(void) {
         fprintf(stderr, "  FAIL: stop note 65\n");
         return 1;
     }
-    safe_usleep(500000);
+    /* Poll until bursts stop increasing (or up to 2 seconds) */
+    int prev = bursts;
+    for (int retries = 0; retries < 20; retries++) {
+        safe_usleep(100000);
+        int cur = bursts;
+        if (cur == prev) break;
+        prev = cur;
+    }
     int bursts_before = bursts;
-    safe_usleep(1000000);
+    safe_usleep(500000);
     int bursts_after = bursts;
     jack_deactivate(client);
     jack_client_close(client);