Arduino Wire.h I2C custom transport on Pi Pico is causing a crash

- Hardware description: Pi Pico
- RTOS: I think arduino mbed
- Version or commit hash: humble

#### Steps to reproduce the issue
I'm trying to make a custom transport for I2C using arduino's Wire library. I am able to build and flash the microros_publisher example, everything works over serial and I can see the topic and node in a docker container. However, when I replace setting the serial transport with my own, I think the pico crashes since i'm getting a flashing pattern on the pico (4 long, 4 0r 5 long). I really hope I'm missing something subtle. Also I'm not sure how I am supposed to properly use `uxr_init_custom_transport`, or if I'm supposed to use it at all, because the default serial transport doesn't. Also if this isn't the correct place to post this issue, please point me in the right direction.

here's my ini

```
env:pico]
platform = https://github.com/maxgerhardt/platform-raspberrypi.git
board = pico
framework = arduino
lib_deps =
https://github.com/micro-ROS/micro_ros_platformio

upload_protocol = mbed

board_microros_distro = humble
board_microros_transport = custom
```

heres the code

https://pastebin.com/5hzPiRcD

Comienza con el ini de PlatformIO y el código de Pastebin enlazado, centrándote en cómo se configura el transporte personalizado y dónde se usa `uxr_init_custom_transport`. Reproduce primero la línea base serie y después el transporte I2C en la Pi Pico; se considera terminado cuando el transporte personalizado ya no bloquea la placa y el nodo y el topic de micro-ROS siguen siendo visibles.

Escrito por el modelo de indexación a partir del texto del issue.