Implement basic stop logic

[Victorbares]

What

Adds stop-sign compliance logic and rewards to the PufferDrive C engine:

• Infraction Logic: Detects stop-sign crossings. Agents must stop (≤ threshold) for ≥ 5 consecutive
  timesteps within 5m of the stop line.
• Z-Axis Validation: Filters out false-positive violations for multi-level roads (e.g. overpasses)
  using Z_BUFFER.
• Config & Metrics: Adds traffic_control_scope to configs and exposes stop_sign_violation_rate and
  reward penalties (sharing the reward_stop_line coefficient) to Python.

Why

• Ensures realistic traffic compliance and prevents unsafe behaviors at intersections while avoiding
  false-positives on stacked/multi-level map geometries.

Notes

• Fully compliant with safety-critical C standards (no malloc/free, zero warnings).
• Shares the existing reward_stop_line coefficient to avoid config bloa