feat(ros-compat): add minimal ROS message conversion with Python example

[guptapratykshh]

#1231
This PR adds a minimal Python API for converting Dora Arrow arrays to ROS message format dictionaries. Sometimes you need to work with ROS message structures in Dora nodes without setting up a full ROS bridge, and this library makes that easy.

Right now it only supports geometry_msgs/Twist, but the structure is simple enough that we can easily add more message types later.

• Library: dora-ros-compat with a simple RosMessageConverter class
• Python API: from dora.ros import RosMessageConverter - converts Arrow arrays to ROS message dicts
• Working example: A complete example showing how to convert Twist messages

[guptapratykshh]

Hi @haixuanTao,

Thanks for the feedback. I have simplified the PR significantly based on your suggestions.

[haixuanTao]

I think one of the main limitation of this implementation is that it doesn't automatically generate message format as the ros2 api and also it is only available in Python

[guptapratykshh]

I have added get_schema() method to automatically generate message formats from ROS definitions, effectively solving the main limitation. The Python-only scope is now explicitly documented as a known constraint in the README.

[haixuanTao]

Can you add an example in the ci that makes a ros1 node talk to a dora node? Like for example the turtle bot example for ros2?

[haixuanTao]

The CI example does not use dora dataflow

[guptapratykshh]

I have updated the CI to run the full dora dataflow (dora start examples/ros-compat/python/ros1_turtle/dataflow.yml) instead of just the unit test. The bridge node now supports a mock mode to allow this full dataflow execution to pass in the CI environment without a running ROS master.