apply go fix for Go 1.26 (#1867)

* apply `go fix` for Go 1.26

This applies the `go fix` recommendations for go1.26

* for all of ./...

routing/balance_test.go

@@ -27,7 +27,7 @@ func TestPacketsAreBalancedEqually(t *testing.T) {
 	gw3count := 0
 
 	iterationCount := uint16(65535)
-	for i := uint16(0); i < iterationCount; i++ {
+	for i := range iterationCount {
 		packet := firewall.Packet{
 			LocalAddr:  netip.MustParseAddr("192.168.1.1"),
 			RemoteAddr: netip.MustParseAddr("10.0.0.1"),
@@ -74,7 +74,7 @@ func TestPacketsAreBalancedByPriority(t *testing.T) {
 	gw2count := 0
 
 	iterationCount := uint16(65535)
-	for i := uint16(0); i < iterationCount; i++ {
+	for i := range iterationCount {
 		packet := firewall.Packet{
 			LocalAddr:  netip.MustParseAddr("192.168.1.1"),
 			RemoteAddr: netip.MustParseAddr("10.0.0.1"),
@@ -115,7 +115,7 @@ func TestBalancePacketDistributsRandomlyAndReturnsFalseIfBucketsNotCalculated(t
 	gw1count := 0
 	gw2count := 0
 
-	for i := uint16(0); i < iterationCount; i++ {
+	for i := range iterationCount {
 		packet := firewall.Packet{
 			LocalAddr:  netip.MustParseAddr("192.168.1.1"),
 			RemoteAddr: netip.MustParseAddr("10.0.0.1"),

routing/gateway.go

@@ -3,6 +3,7 @@ package routing
 import (
 	"fmt"
 	"net/netip"
+	"strings"
 )
 
 const (
@@ -13,14 +14,14 @@ const (
 type Gateways []Gateway
 
 func (g Gateways) String() string {
-	str := ""
+	var str strings.Builder
 	for i, gw := range g {
-		str += gw.String()
+		str.WriteString(gw.String())
 		if i < len(g)-1 {
-			str += ", "
+			str.WriteString(", ")
 		}
 	}
-	return str
+	return str.String()
 }
 
 type Gateway struct {