fix: simplify diag_timer_cb — use pool->free_count instead of allocations-reuse

DIAG line now shows clear metrics:
  rq/wq — queue sizes
  ent_f/dat_f — free_count of entry/data pools (→0 = leak)
  wbuf — partial send stuck
  tcp_rb/tcp_sb — kernel socket buffers

src/proxy/tcp_proxy_server.c

@@ -129,9 +129,8 @@ static void diag_timer_cb(void* arg) {
     struct tcp_conn* tc = rc->tc;
     if (!tc || tc->sock == SOCKET_INVALID) return;
 
-    size_t ea, er, da, dr;
-    memory_pool_get_stats(tc->entry_pool, &ea, &er);
-    memory_pool_get_stats(tc->data_pool,  &da, &dr);
+    int ent_f = tc->entry_pool->free_count;
+    int dat_f = tc->data_pool->free_count;
 
     int rcv_buf = 0, snd_buf = 0;
     socklen_t optlen = sizeof(int);
@@ -139,16 +138,15 @@ static void diag_timer_cb(void* arg) {
     getsockopt(tc->sock, SOL_SOCKET, SO_SNDBUF, &snd_buf, &optlen);
 
     DEBUG_INFO(DEBUG_CATEGORY_SOCKET,
-        "SOCK:DIAG fd=%d sid=%08x conn=%d err=%d fin=%d "
-        "rpaused=%d wmon=%d rq=%d(%zdb) wq=%d(%zdb) wbuf=%s "
-        "entry=%zd data=%zd tcp_rb=%d tcp_sb=%d",
-        (int)tc->sock, rc->stream_id, tc->connected, tc->error, tc->fin,
-        tc->read_paused, tc->write_monitor,
+        "SOCK:DIAG fd=%d sid=%08x conn=%d fin=%d "
+        "rq=%d(%zub) wq=%d(%zub) wbuf=%s "
+        "ent_f=%d dat_f=%d tcp_rb=%zu tcp_sb=%zu",
+        (int)tc->sock, rc->stream_id, tc->connected, tc->fin,
         tc->read_queue->count,  queue_total_bytes(tc->read_queue),
         tc->write_queue->count, queue_total_bytes(tc->write_queue),
         tc->write_buf ? "y" : "n",
-        (ssize_t)(ea - er), (ssize_t)(da - dr),
-        rcv_buf, snd_buf);
+        ent_f, dat_f,
+        (size_t)rcv_buf, (size_t)snd_buf);
 
     rc->diag_timer = uasync_set_timeout(rc->ua, 10000, rc, diag_timer_cb, "tps_diag");
 }