Add MQTT GPIO control and status topics

[fpoisson2]

Implement dedicated MQTT topics for GPIO control:

• Subscribe to msh/{root}/2/gpio/{NODE_ID}/control for commands
• Publish status to msh/{root}/2/gpio/{NODE_ID}/status

Supported JSON command formats:

• Simple: {"pin": N, "value": V} or {"pin": N, "command": "read"}
• Advanced: {"command": "write/read/watch", "gpio_mask": M, "gpio_value": V}

Status response format:
{"type":"gpio_status","gpio_mask":M,"gpio_value":V,"timestamp":T,"node_id":"!xxx"}

The RemoteHardwareModule now publishes GPIO status to MQTT when:

• GPIO write commands are executed
• GPIO read responses are sent
• Watched GPIOs change state

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• I have tested that my proposed changes behave as described.
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  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
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[fifieldt]

Cool idea :) Are you in discord? It's probably worth some discussion about whether it's safe to enable this by default, or whether we need a protobuf to turn it on/off.

[phaseloop]

why this part is NRF52 specific? Also condition - "if nrf52 is not defined or nrf52 uses json" is weird. Should it be "if nrf52 is defined AND uses json"?

[phaseloop]

It seems this code was made by AI. Along with my comment above about weird NRF52 condition that does not make sense - I suppose this should be double checked and threaded with caution.