fix: apply lossless push in PoolObjectNode too

PoolNode and PoolObjectNode each have their own push_one_out(). The previous
commit only reached PoolNode's copy, so ObjectNode-based pipelines — the common
case — still dropped on overflow with lossless enabled.

Verified end to end: a 2300-frame source now reports exactly 2300 frames at
every stage, where it previously delivered 774 to the second node.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

include/kpn/pool_node.hpp

@@ -732,6 +732,11 @@ private:
             ch->push_sentinel(std::move(val));
             return;
         }
+        // Lossless mode: block until the consumer drains instead of dropping.
+        if (lossless_) {
+            ch->push_blocking(std::move(val));
+            return;
+        }
         try {
             ch->push(std::move(val));
         } catch (const ChannelOverflowError&) {