feat: Grouping the traffic lights

[plass-bertrandt]

Reference to a related issue in the repository

TrafficLight rework proposal. #754

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The individual bulbs of a traffic light rarely function as standalone signals. Rather, they form a unit consisting of two or three bulbs that convey a specific instruction to the driver.

The introduction of the group_id defines a unique assignment of the lights. It replaces heuristics—such as those based on position and orientation—that were previously necessary in the user software.

Some questions to ask:

• It's a new feature.
• Backward compatibility:

  IF group_id IS PRESENT:
      → Group bulbs by group_id
  ELSE:
      → Fall back to position-based / heuristic grouping (legacy)
  

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