shard object has to be copied from the SM when sending raft messages

[lni]

See link below

matrixcube/raftstore/replica_event_raft_ready.go

Line 183 in 5e47a03

func (pr *replica) sendRaftMessage(msg raftpb.Message) error {

Another related question is whether it is possible to avoid including the Epoch value in the raft message.