[client/idd] input: reduce network latency

Route input through a dedicated high-priority stream, send pointer
motion as cumulative datagrams, and recover suspected loss reliably.

Reduce downstream input queuing with age-aware coalescing and input
thread scheduling.

client/transports/Network/input.h

@@ -37,5 +37,9 @@ void networkInputDestroy(NetworkInput ** input);
 const LG_InputOps * networkInputGetOps(void);
 
 void networkInputConnectionState(NetworkInput * input, bool connected);
+void networkInputSendReady(NetworkInput * input,
+    NetworkPacketDelivery delivery);
+void networkInputDatagramLost(NetworkInput * input,
+    uint64_t claimEpoch, uint64_t pointerSequence);
 bool networkInputPacket(NetworkInput * input,
     const LGNetPacketView * packet, bool datagram);