[idd] clipboard: batch helper stream delivery

Extend the clipboard target boundary with ordered prefix delivery.
Pass up to four queued LGMP stream records to the Helper ring in one
operation, apply state only to the accepted prefix, and retain the
remaining suffix for exact retries.

The channel holds its write lock across the prefix and emits one pipe
doorbell per stream window instead of one per record.

idd/LGIdd/transport/CClipboardHub.h

@@ -73,6 +73,9 @@ public:
   ClipboardChannelResult SendClipboard(
     const KVMFRClipboardMessage& record,
     const uint8_t * data) override;
+  ClipboardChannelResult SendClipboardBatch(
+    const ClipboardChannelWrite * records,
+    size_t count, size_t& accepted) override;
   void ClipboardReceiveReady() override;
   void ClipboardFailed() override;
 };