feat(mqtt): implement deferred OTA update scheduling in MyMesh

Add functionality to schedule deferred OTA updates in the MyMesh class.
This includes a new member variable to track the update time and a method
to initiate the update process, allowing for a smoother OTA experience
by managing timing and state transitions effectively.

examples/simple_room_server/MyMesh.cpp

@@ -1374,6 +1374,23 @@ void MyMesh::loop() {
     MESH_DEBUG_PRINTLN("Radio params restored");
   }
 
+#if defined(WITH_MQTT_BRIDGE) && defined(OTA_MANIFEST_BASE)
+  if (_ota_update_at && millisHasNowPassed(_ota_update_at)) { // deferred `ota update`
+    _ota_update_at = 0;                                       // clear timer
+    // The "Beginning update..." reply has now gone out. Free the bridge for heap
+    // headroom, then flash: otaFromManifest reboots into the new image on success
+    // (so this never returns); on any abort (already up to date, partition change,
+    // download error) it returns and we resume the bridge.
+    Serial.println("OTA: starting update");
+    setBridgeState(false);
+    char ota_reply[160];
+    if (!_cli.getBoard()->otaFromManifest(getFirmwareVer(), false, ota_reply)) {
+      Serial.print("OTA: aborted, resuming bridge - "); Serial.println(ota_reply);
+      setBridgeState(true);
+    }
+  }
+#endif
+
   // is pending dirty contacts write needed?
   if (dirty_contacts_expiry && millisHasNowPassed(dirty_contacts_expiry)) {
     acl.save(_fs, MyMesh::saveFilter);

examples/simple_room_server/MyMesh.h

@@ -125,6 +125,7 @@ class MyMesh : public mesh::Mesh, public CommonCLICallbacks {
   RegionEntry* recv_pkt_region;
   TransportKey default_scope;
   unsigned long set_radio_at, revert_radio_at;
+  unsigned long _ota_update_at = 0;  // deferred `ota update` fire time (0 = none scheduled)
   float pending_freq;
   float pending_bw;
   uint8_t pending_sf;
@@ -352,6 +353,15 @@ public:
 #endif
   }
 
+  // Schedule the pull-OTA flash to run from loop() in ~2.5 s, leaving time for the
+  // "Beginning update..." CLI reply (CLI_REPLY_DELAY_MILLIS = 600 ms) to transmit
+  // before the flash blocks the loop and reboots.
+  bool beginDeferredOtaUpdate() override {
+    _ota_update_at = millis() + 2500;
+    if (_ota_update_at == 0) _ota_update_at = 1;  // 0 means "none"
+    return true;
+  }
+
   int getQueueSize() override {
     return bridge ? bridge->getQueueSize() : 0;
   }