Feature: Seamless Cross-Preset Communication via UDP Multicast Bridging (#7753)

* Added compatibility between nodes on different Presets through `Mesh via UDP`

* Optimize multicast handling and channel mapping

- FloodingRouter: remove redundant UDP-encrypted rebroadcast suppression.
- Router: guard multicast fallback with HAS_UDP_MULTICAST and map fallback-decoded packets
  to the local default channel via isDefaultChannel()
- UdpMulticastHandler: set transport_mechanism only after successful decode

* trunk fmt

* Move setting transport mechanism.

---------

Co-authored-by: GUVWAF <thijs@havinga.eu>

src/mesh/udp/UdpMulticastHandler.h

@@ -50,10 +50,10 @@ class UdpMulticastHandler final
         LOG_DEBUG("UDP broadcast from: %s, len=%u", packet.remoteIP().toString().c_str(), packetLength);
 #endif
         meshtastic_MeshPacket mp;
-        mp.transport_mechanism = meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP;
         LOG_DEBUG("Decoding MeshPacket from UDP len=%u", packetLength);
         bool isPacketDecoded = pb_decode_from_bytes(packet.data(), packetLength, &meshtastic_MeshPacket_msg, &mp);
         if (isPacketDecoded && router && mp.which_payload_variant == meshtastic_MeshPacket_encrypted_tag) {
+            mp.transport_mechanism = meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP;
             mp.pki_encrypted = false;
             mp.public_key.size = 0;
             memset(mp.public_key.bytes, 0, sizeof(mp.public_key.bytes));