feat: enhance tariff processing with error handling and category filtering

pkg/utils/utils.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"hash/fnv"
 	"math"
+	"strconv"
 
 	"github.com/golang-jwt/jwt/v5"
 )
@@ -123,3 +124,10 @@ func HashArray[T Hashable](arr []T) (string, error) {
 
 	return fmt.Sprintf("%x", h.Sum64()), nil
 }
+
+func IsDigit(v string) (bool, *int64) {
+	if val, err := strconv.ParseInt(v, 10, 64); err == nil {
+		return true, &val
+	}
+	return false, nil
+}