Canned Messages via InkHUD menu (#7096)

* Allow observers to respond to AdminMessage requests
Ground work for CannedMessage getters and setters

* Enable CannedMessage config in apps for InkHUD devices

* Migrate the InkHUD::Events AdminModule observer
Use the new AdminModule_ObserverData struct

* Bare-bones NicheGraphics util to access canned messages
Handles loading and parsing. Handle admin messages for setting and getting.

* Send canned messages via on-screen menu

* Change ThreadedMessageApplet from Observer to Module API
Allows us to intercept locally generated packets ('loopbackOK = true'), to handle outgoing canned messages.

* Fix: crash getting empty canned message string via Client API

* Move file into Utils subdir

* Move an include statement from .cpp to .h

* Limit strncpy size of dest, not source
Wasn't critical in ths specific case, but definitely a mistake.

src/graphics/niche/InkHUD/Applets/User/ThreadedMessage/ThreadedMessageApplet.h

@@ -30,7 +30,7 @@ namespace NicheGraphics::InkHUD
 
 class Applet;
 
-class ThreadedMessageApplet : public Applet
+class ThreadedMessageApplet : public Applet, public SinglePortModule
 {
   public:
     explicit ThreadedMessageApplet(uint8_t channelIndex);
@@ -41,16 +41,11 @@ class ThreadedMessageApplet : public Applet
     void onActivate() override;
     void onDeactivate() override;
     void onShutdown() override;
-    int onReceiveTextMessage(const meshtastic_MeshPacket *p);
+    ProcessMessage handleReceived(const meshtastic_MeshPacket &mp) override;
 
     bool approveNotification(Notification &n) override; // Which notifications to suppress
 
   protected:
-    // Used to register our text message callback
-    CallbackObserver<ThreadedMessageApplet, const meshtastic_MeshPacket *> textMessageObserver =
-        CallbackObserver<ThreadedMessageApplet, const meshtastic_MeshPacket *>(this,
-                                                                               &ThreadedMessageApplet::onReceiveTextMessage);
-
     void saveMessagesToFlash();
     void loadMessagesFromFlash();