Support iterable ROS arguments in Node

[Old-Ding]

Summary

• materialize Node.ros_arguments at the command construction boundary
• support generators, iterators, tuples, and other finite iterables promised by the public annotation
• run the existing ROS argument launch test with an iterator

Testing

• focused expression probe: baseline list concatenation raises TypeError for an iterator, while the fixed expression preserves argument order
• python -m py_compile for both modified Python files
• flake8 on both modified files with the repository's existing E501/W504 exclusions
• git diff --check

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