fix: []byte nil resp && feature: add WriteBulkFrom with bufio.Writer for Conn interface WriteBulkFrom func

[weedge]

1. fix: []byte nil resp // resp "" "" Expect nil, nil arr := [][]byte{nil, nil} conn.WriteAny(arr)

   // need change tmp := []interface{}{} for i := range arr { if arr[i] == nil { tmp = append(tmp, nil) continue } tmp = append(tmp, arr[i]) } conn.WriteAny(tmp)

so when check []byte, if is nil, AppendNull resp

2. add WriteBulkFrom with bufio.Writer for Conn interface WriteBulkFrom func