Fix dangling callback reference and sim ESP-NOW channel reliability

[Copilot]

Two bugs introduced in the channel discovery PR: a dangling reference UAF in the receiver's discovery callback, and a broken sim ESP-NOW transport that only delivered packets to one process per port.

ReceiverApp: RAII guard for onDiscoveryResponse callback

runChannelDiscovery() registered a callback capturing a reference to a stack-local ChannelScanner. The callback outlived the scanner, creating a UAF on the next discovery cycle.

Fixed with a local RAII guard that clears the callback at every exit point (C++ destruction order guarantees the guard runs before the scanner):

_radio.onDiscoveryResponse([&scanner](...) { scanner.onDiscoveryResponse(...); });
struct DiscoveryResponseGuard {
    ReceiverRadioLink &radio;
    ~DiscoveryResponseGuard() { radio.onDiscoveryResponse(nullptr); }
} cbGuard{_radio};

sim_espnow: UDP multicast + thread-safe channel switching

• Unicast → multicast per channel (239.0.0.<ch>:<port>): SO_REUSEPORT unicast delivers to only one socket under kernel load-balancing, breaking multi-process sim scenarios. Each process now joins the multicast group via IP_ADD_MEMBERSHIP on loopback; esp_now_send() targets the group address.
• Thread-safe rebind: sim_set_wifi_channel() previously closed/reopened the socket while recvLoop was live. Now stops the thread with pthread_join() (error-checked) before touching the socket, then restarts it.

cmd_io: Fix incorrect cppcheck suppression

txCmdModule had // cppcheck-suppress constParameterCallback but the actual warning is constParameterPointer. Corrected to match the emitted diagnostic.

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[Copilot]

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[Copilot]

Pull request overview

Dieses PR behebt zwei Regressionen aus dem Channel-Discovery-Feature: einen Use-after-free durch einen langlebigen Discovery-Callback im Receiver sowie unzuverlässiges Paket-Fanout in der nativen ESP-NOW-Simulation durch Wechsel von UDP-Unicast auf Multicast.

Changes:

• Receiver: RAII-Guard, der den onDiscoveryResponse-Callback beim Verlassen von runChannelDiscovery() zuverlässig zurücksetzt (verhindert dangling reference auf stack-lokalen ChannelScanner).
• Simulation: ESP-NOW-Transport auf UDP-Multicast pro Kanal umgestellt und Channel-Switch so angepasst, dass der Receive-Thread vor Rebind gestoppt/restarted wird.
• Transmitter Shell: cppcheck-Suppression-Tag auf die tatsächlich gemeldete Warnung angepasst.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
firmware/src/transmitter/shell/cmd_io.cpp	Korrigiert cppcheck-Suppression auf den passenden Warnungsnamen.
firmware/src/receiver/ReceiverApp.cpp	Fügt Scope-Guard hinzu, der Discovery-Callback beim Return löscht und so UAF verhindert.
firmware/sim/src/sim_espnow.cpp	Wechselt auf Multicast pro Kanal und implementiert Thread-Stop/Restart beim Channel-Wechsel.