Link OpenDRIVE signals to intersection maneuvers

[aprabou]

Description

• Add Maneuver.signal and Signal.controlledManeuvers so each junction movement can reference its controlling signal (and vice versa).
• Wire the link during OpenDRIVE conversion using connecting-road signals first (by lane validity), then incoming-road approach signals.
• Add self-contained integration tests (inline .xodr fixtures) covering per-lane validity, approach fallback, T-junction distinct signals, and unsignalized junctions.

Checklist

• I have tested the changes locally via pytest and/or other means
• I have added or updated relevant documentation
• I have autoformatted the code with black and isort
• I have added test cases (if applicable)

[aprabou]

Parse OpenDRIVE 1.8+ <semantics><priority type="…"/> and expose it on domain Signal via an optional SignalPriorityType enum and priorities tuple. Classification prefers priorities when present; otherwise falls back to CARLA/OpenDRIVE type codes (1000001 traffic light, 206 stop, 205 yield). Also pass through subtype, propagate priorities through signalReference, and warn once when a known legacy type disagrees with <priority>.