Implement tiered pathfinding with thread-local scratchpads

- TIER0 (<10 tiles): Vec-based linear search, zero hash overhead
- TIER1 (10-30 tiles): FxHashMap scratchpad with memory reuse
- TIER2 (30-100 tiles): AHashMap scratchpad for better collision resistance
- TIER3 (>100 tiles): Chunk waypoint decomposition
- Added benchmarking infrastructure with F8 report trigger
- Added async infrastructure: PendingPath, CompletedPaths resources
- Lowered MAX_NODES to 5000 to prevent runaway searches

Benchmarks show P50 improved 13%, max improved 53%

src/entities/shared_components/ambulatory.rs

@@ -9,3 +9,21 @@ pub struct Ambulatory {
     pub target: Option<Vec3>,
     pub step_recovery: u32,
 }
+
+#[derive(Component)]
+pub struct PendingPath {
+    pub start: IVec3,
+    pub goal: IVec3,
+    pub waypoint_path: Vec<Vec3>,
+    pub request_id: u64,
+}
+
+#[derive(Resource, Default)]
+pub struct PathRequestCounter {
+    pub next_id: u64,
+}
+
+#[derive(Resource, Default)]
+pub struct CompletedPaths {
+    pub paths: Vec<(u64, Vec<Vec3>)>,
+}