[client] transport: introduce pluggable frame transports

Move shared-memory ownership, LGMP session handling, queue access, and
DMA setup behind a transport interface. The LGMP backend preserves the
existing zero-copy frame and DMA paths while owning its lgmp:* options.

Expose the initialized EGL context through a versioned renderer interop
record for future accelerated decode backends. Add an LGMP-independent,
deterministic test transport for graphics-pipeline validation.

client/src/keybind.c

@@ -128,7 +128,7 @@ static void bind_toggleKey(int sc, void * opaque)
 
 static void bind_setGuestRes(int sc, void * opaque)
 {
-  if (!(g_state.kvmfrFeatures & KVMFR_FEATURE_WINDOWSIZE))
+  if (!(g_state.transportFeatures & LG_TRANSPORT_FEATURE_WINDOW_SIZE))
   {
     app_alert(LG_ALERT_INFO, "The guest doesn't support this feature");
     return;