Refactoring goals

[vcharraut]

What

Rewrites the target/waypoint system into a single, direct goal abstraction.

Removed the intermediate Path/Waypoint layer:

• Dropped struct Path, struct Waypoint, MAX_NUM_WP_PATH (200-point densification), build_path, get_closest_waypoint_index_on_path, path_progression, closest_path_idx_wp, num_waypoints_reached.
• Goals are now sampled directly at spacings along the route/map — no per-agent 200-waypoint buffer.

New goal model (datatypes.h):

• Flat goal list list_goal_{x,y,z}[MAX_GOALS] + list_goal_lane[], with current_goal_* aliases, goal_count, and gt_goal_* (ground-truth goal pin for replay).
• Agent.current_route_index → current_route_idx.

New generation / regeneration pipeline (drive.h): chain_goals → commit_goals, generate_new_goals_from_route, generate_new_goals_from_map, roll_goals, route_point_at_distance, compute_new_route.

Lane-graph GPS distance: LaneGraph.lane_to_graph_idx (road-element idx → graph idx) enables appending normalized lane-graph distance-to-goal on lane obs rows.

Config (drive.ini / env_config.h) — renamed/replaced:

• target_type (static/dynamic) → goal_regen_mode (finite = regen full set once all reached / rolling = sliding window).
• goal_on_lane → goal_source (route = agent forward route / map = uniform free-roam).
• num_target_waypoints → num_goals; min/max_waypoint_spacing → min/max_goal_spacing.
• New obs_goal_lane_distance flag.

Lane/boundary observation unpacking capped to the first 7 elements per row; obs feature counts adjusted accordingly. Notebooks, viz.py, torch.py, tests, and rollout/smoke golden data updated to match.

🤖 Generated with Claude Code

[vcharraut]

Split into two stacked PRs for reviewability:

• Rename goal/route identifiers (no behavior change) #511 — pure identifier renames (no behavior change), base 3.0
• Goal-system rewrite: direct goal sampling (replaces Path/Waypoint) #512 — goal-system rewrite, stacked on Rename goal/route identifiers (no behavior change) #511

Superseded by those; can be closed once #511/#512 are reviewed.