Serial bus No. 3: Configure peers over Serial Bus

[JensOgorek]

Motivation

When configuring ESP32 nodes over the serial bus, there was no easy way to send a complete .liz script to a remote node. Additionally, if a broken script was deployed to a bus node (or a script without SerialBus configuration), the node would become unreachable and require physical USB access to fix.

Implementation

Remote configuration via serial bus (configure.py)

• Added --serial-bus NODE_ID argument
• Wraps each command in bus.send(NODE_ID, '...') to forward to remote node
• Waits for reboot and verifies checksum via bus echo relay

String quoting in expression output (expression.cpp)

• Strings containing " are now output with single quotes instead of double quotes
• This allows commands like core.output("core.millis module1.property1") to be sent via bus.send(node, '...') without breaking the quoting

Automatic bus backup (main/utils/bus_backup.cpp)

• When a SerialBus is created, its config (pins, baud, uart, node_id) is saved to NVS
• On boot, if the startup script fails to create a SerialBus but backup config exists:
  • Removes all existing Serial modules
  • Creates a fresh Serial and SerialBus from the saved backup config
  • This keeps the node reachable over the bus even with a broken startup script
• Added core.forget_serial_bus() to clear the saved config from NVS

Design Decisions

• expression.cpp — no handling for strings with both " and ': not needed since the quoting is only used by configure.py in a controlled context.
• serial_bus.h — serial and node_id moved to public: fine since both are const, simple and safe.
• restore_if_needed() removes all Serial modules (not just the bus one): acceptable trade-off since keeping the node reachable is the priority.

Progress

• The implementation is complete.
• Tested on hardware.
• Documentation has been added.

[JensOgorek]

Tested with

Working bus peer id1 script

rdyp = Output(15)
en3 = Output(12)

serial = Serial(26, 27, 115200, 1)
bus = SerialBus(serial,1)

testi = Input(32)

core.output("core.millis")
core.mute()

rdyp.on()
en3.on() 

unreachable bus peer id1 script

rdyp = Output(15)
en3 = Output(12)

testi = Input(32)

// these create serial on different pins and no bus is created.
serial_bad = Serial(25,26,115200,1) 
serial_bad2 = Serial(27,14,115200,2)

core.output("core.millis")
core.mute()

rdyp.on()
en3.on() 

After the first script was configured first, the backup was created. On the second script, lizard removed both serial modules and created a fresh serial with bus from the backup, so the esp32 on the bus was still reachable.

[falkoschindler]

I (manually) reviewed the PR and added some comments. Let's address them first before checking the final result one last time.

[falkoschindler]

Apart from improving print_to_buffer, can you look into the conflicts with main? Thanks!