No more Singleton

I hate this singleton stuff. Now Z2MDevice have a gateway (not really
nice but can be usefull)

gateway.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"log/slog"
 	"slices"
-	"sync"
 
 	MQTT "github.com/eclipse/paho.mqtt.golang"
 	"gitlab.imt-atlantique.fr/xaal/code/go/core/xaal"
@@ -17,20 +16,8 @@ type Gateway struct {
 	config  *Config
 }
 
-var (
-	instance *Gateway
-	once     sync.Once
-)
-
-func GetGW() *Gateway {
-	once.Do(func() {
-		instance = &Gateway{devices: make(map[string]*Z2MDevice)}
-	})
-	return instance
-}
-
 func NewGW(cfg *Config, eng *xaal.Engine) *Gateway {
-	gw := GetGW()
+	gw := &Gateway{devices: make(map[string]*Z2MDevice)}
 	gw.config = cfg
 	gw.client = mqttSetup(cfg, gw.mqttPublishHander)
 	// NOTE: Wondering if we can setup engine before
@@ -44,6 +31,12 @@ func (gw *Gateway) GetZDevice(name string) *Z2MDevice {
 
 func (gw *Gateway) AddZDevice(zDev *Z2MDevice) {
 	gw.devices[zDev.FriendlyName] = zDev
+	zDev.Gateway = gw
+}
+
+func (gw *Gateway) RemoveZDevice(zDev *Z2MDevice) {
+	zDev.Gateway = nil
+	delete(gw.devices, zDev.FriendlyName)
 }
 
 func (gw *Gateway) GetZDevices() map[string]*Z2MDevice {

z2m.go

@@ -35,6 +35,7 @@ type Z2MDevice struct {
 	SwBuildID    string `json:"software_build_id"`
 	FriendlyName string `json:"friendly_name"`
 	XAALDevices  []XAALDeviceInterface
+	Gateway      *Gateway
 }
 
 type Expose struct {
@@ -137,7 +138,7 @@ func (zDev *Z2MDevice) setupXAALDevices(gw *Gateway) {
 func (zDev *Z2MDevice) Publish(topic string, payload interface{}) {
 	topic = zDev.getTopic() + "/" + topic
 	slog.Debug("Sending", "topic", topic, "payload", payload)
-	client := GetGW().client
+	client := zDev.Gateway.client
 	if token := client.Publish(topic, 0, false, payload); token.Wait() && token.Error() != nil {
 		slog.Error("PUBLISH Error", ":", token.Error())
 	}