docs: late_resequenced counts held-then-delivered packets, not gaps avoided

Fix the false trailing clause in the udps_stats_t::late_resequenced comment,
move udps_held_t from the tunable-limits section to internal-state next to
udps_slot_t, and add braces to three braceless if bodies to match house style.

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

deps/udpsclient/udps_client.h

@@ -188,8 +188,12 @@ typedef struct {
      */
     uint64_t stale_packets;
     /**
-     * DATA packets that arrived out of order and were put *back* in order inside
-     * the reorder window, so the consumer never saw a gap for them.
+     * DATA packets that were held waiting for an earlier counter and subsequently
+     * delivered via @c drain_held().  This includes a packet released by the
+     * reorder window expiring: that packet arrives alongside a non-zero @c lost
+     * and therefore alongside a gap, so @c late_resequenced is not by itself a
+     * count of gaps avoided.  Compare @c late_delivered, which counts packets
+     * that lost the race past an already-expired window entirely.
      */
     uint64_t late_resequenced;
     /**