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