all: apply go fix

Updates #cleanup

Signed-off-by: Adriano Sela Aviles <adriano@tailscale.com>

tstest/natlab/vmtest/tailmac.go

@@ -428,11 +428,11 @@ func waitForVMIP(t testing.TB, mac string, timeout time.Duration) (string, error
 			var currentIP string
 			for _, line := range lines {
 				line = strings.TrimSpace(line)
-				if strings.HasPrefix(line, "ip_address=") {
-					currentIP = strings.TrimPrefix(line, "ip_address=")
+				if after, ok := strings.CutPrefix(line, "ip_address="); ok {
+					currentIP = after
 				}
-				if strings.HasPrefix(line, "hw_address=") {
-					hw := strings.TrimPrefix(line, "hw_address=")
+				if after, ok := strings.CutPrefix(line, "hw_address="); ok {
+					hw := after
 					if strings.ToLower(hw) == leaseMAC && currentIP != "" {
 						return currentIP, nil
 					}

tstest/natlab/vmtest/vmtest.go

@@ -872,7 +872,7 @@ func (e *Env) BringUpMullvadWGServer(n *Node, gw netip.Prefix, listenPort uint16
 		e.t.Fatalf("BringUpMullvadWGServer(%s): %s: %s", n.name, res.Status, body)
 	}
 	var pubB64 string
-	for _, line := range strings.Split(string(body), "\n") {
+	for line := range strings.SplitSeq(string(body), "\n") {
 		if s, ok := strings.CutPrefix(strings.TrimSpace(line), "PUBKEY="); ok {
 			pubB64 = s
 			break
@@ -2046,7 +2046,7 @@ func findKernelPath(goMod string) (string, error) {
 	goModCache := strings.TrimSpace(string(goModCacheB))
 
 	// Parse go.mod to find gokrazy-kernel version.
-	for _, line := range strings.Split(string(b), "\n") {
+	for line := range strings.SplitSeq(string(b), "\n") {
 		line = strings.TrimSpace(line)
 		if strings.HasPrefix(line, "github.com/tailscale/gokrazy-kernel") {
 			parts := strings.Fields(line)