promql/functions.go
func funcIdelta(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	return instantValue(vals, enh.out, false)
}
func funcIdelta(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	return instantValue(vals, enh.out, false)
}
// === idelta(node model.ValMatric) Vector ===