item.go
func ItemSize(p unsafe.Pointer) int {
	itm := (*Item)(p)
	return int(itemHeaderSize + uintptr(itm.dataLen))
}
func ItemSize(p unsafe.Pointer) int {
	itm := (*Item)(p)
	return int(itemHeaderSize + uintptr(itm.dataLen))
}
// ItemSize returns total bytes consumed by item representation