feat(pathfinding): implement hierarchical task-based pathfinding
Phase 1 - Chunk-Graph Layer:
- Add world_to_chunk, chunk_to_world, get_chunk_neighbors helpers
- Add update_chunk_connectivity system to build chunk adjacency graph
- Implement calculate_chunk_path for macro A* on chunk coordinates
- Wire hierarchical tier dispatch into prepare_paths
Phase 2 - Async Infrastructure (ready for integration):
- Add StandableTileSnapshot for chunk-local tile data copy
- Add AsyncPathTask component for Task handle storage
- Add spawn_async_path_task and poll_async_path_tasks functions
Performance improvements:
- Before: avg=418µs, median=175µs, max=80ms, p95=791µs
- After: avg=244µs, median=140µs, max=16ms, p95=355µs
- 87% reduction in tail latency, 41% faster average
popertots
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