[client] egl: snapshot DMA frames before release

Copy imported IVSHMEM frames into renderer-owned textures before
acknowledging their LGMP messages. Hold each lease until its copy fence
signals, and protect selected snapshots until rendering completes.

Track independent delivery lanes, drain acknowledgements on the frame
thread, and recover stale queue subscriptions after host timeouts.

client/include/interface/transport.h

@@ -145,6 +145,12 @@ typedef struct LG_TransportFrame
   int dmaFD;
   const FrameDamageRect * damageRects;
   uint32_t damageRectsCount;
+
+  /* A transport may keep the frame payload alive asynchronously after
+   * onFrame returns. The callback is idempotent and releases that ownership. */
+  LG_FrameReleaseFn releaseFn;
+  void            * releaseOpaque;
+  uint64_t          releaseHandle;
 }
 LG_TransportFrame;