Build a traffic light

• Three lights, with only the active one lit
• The cycle is red, green, yellow, then back to red, with a separate duration per light supplied through a config prop or object
• The sequence is modelled as a state machine (a config of state -> { duration, next }), not as a chain of nested timeouts
• A timer is set for the current state only and is cleared when the state changes or the component unmounts
• Changing the durations while mounted takes effect from the next transition without breaking the cycle
• Accessible: the current state is exposed as text or aria-label (for example "Traffic light: green")

Only after every requirement works.

• Pause and resume, and a manual "next" button
• A pedestrian-crossing button that requests red at the next opportunity
• A countdown showing seconds left for the current light