pin 0 on RP2040 is not accepted as stepper auto-zero pin

[tigert]

Describe the bug
Steppers let you describe a pin for limit switch, so that mobiflight knows the zero point without manual calibration.

Steps To Reproduce
Steps to reproduce the behavior:

1. Click on Add stepper device in MF Modules and with your RP Pico selected
2. Set the pins, and set auto zero switch to pin 0.
3. Click on the board name and again the stepper device
4. Observe the auto zero [x] None checkbox became checked again. This happens only on pin 0.

Expected behavior
Should allow all valid pins as auto zero pin.

"The Revelation", aka "oh crap..."
Actually the problem is not trivial to fix. We use "0" to mark "no auto-zero pin is set" it seems, because before RP2040 or ProMicro, GPIO 0 and 1 were never available since they are the USB serial port in most Arduinos.

So I guess there is a problem that setting it to zero, makes MF Connector assume the pin was unset, but even when it is saved to the eeprom, the firmware also interprets it as "no pin is set".

Details

• MobiFlight Version: 10.4.0.1
• FlightSim: irrelevant
• AddOn: irrelevant

Additional context
Touches also MobiFlight-Firmware side.