all: use Go 1.26 things, run most gofix modernizers

I omitted a lot of the min/max modernizers because they didn't
result in more clear code.

Some of it's older "for x := range 123".

Also: errors.AsType, any, fmt.Appendf, etc.

Updates #18682

Change-Id: I83a451577f33877f962766a5b65ce86f7696471c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/k8s-operator/egress-services_test.go

@@ -243,7 +243,7 @@ func portsForEndpointSlice(svc *corev1.Service) []discoveryv1.EndpointPort {
 		ports = append(ports, discoveryv1.EndpointPort{
 			Name:     &p.Name,
 			Protocol: &p.Protocol,
-			Port:     pointer.ToInt32(p.TargetPort.IntVal),
+			Port:     new(p.TargetPort.IntVal),
 		})
 	}
 	return ports