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%

Cargo.lock

@@ -2331,10 +2331,12 @@ dependencies = [
 name = "dorf"
 version = "0.1.0"
 dependencies = [
+ "ahash",
  "bevy",
  "bevy_platform",
  "bevy_rand",
  "image",
+ "nohash-hasher",
  "noise",
  "rand 0.10.0",
  "rayon",
@@ -3567,6 +3569,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "nohash-hasher"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2bf50223579dc7cdcfb3bfcacf7069ff68243f8c363f62ffa99cf000a6b9c451"
+
 [[package]]
 name = "noise"
 version = "0.9.0"