promql/functions.go
func funcLn(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	return simpleFunc(vals, enh, math.Log)
}
func funcLn(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	return simpleFunc(vals, enh, math.Log)
}
// === ln(Vector ValueTypeVector) Vector ===