Wrap TileMap HashMaps in Arc for async pathfinding access

- Add Arc<AHashMap> wrapper around floor_tiles, fixture_tiles, item_tiles
- Copy-on-write semantics: Arc::make_mut clones only if other Arcs exist
- Add insert_floor, insert_fixture, insert_item, remove_item methods
- Add get_floor_mut, get_fixture_mut for visibility updates
- Update all mutation sites to use new TileMap methods
- Enables cheap Arc::clone for async pathfinding workers
- Single-threaded pathfinding: no clone, direct access
- Multi-threaded pathfinding: clone Arc, read without locks

src/entities/item/prefabs/misc/misc_prefabs.rs

@@ -41,15 +41,7 @@ pub fn spawn_prefab(
                     },
                 })
                 .id();
-            let mut items = tilemap
-                .item_tiles
-                .get(&position.as_ivec3())
-                .unwrap_or(&Vec::new())
-                .clone();
-            items.push(meat.index_u32());
-            tilemap
-                .item_tiles
-                .insert(position.as_ivec3(), items.clone());
+            tilemap.insert_item(position.as_ivec3(), meat.index_u32());
             return commands
                 .entity(meat)
                 .insert(VisibleGameEntity)
@@ -76,15 +68,7 @@ pub fn spawn_prefab(
                     },
                 })
                 .id();
-            let mut items = tilemap
-                .item_tiles
-                .get(&position.as_ivec3())
-                .unwrap_or(&Vec::new())
-                .clone();
-            items.push(coin.index_u32());
-            tilemap
-                .item_tiles
-                .insert(position.as_ivec3(), items.clone());
+            tilemap.insert_item(position.as_ivec3(), coin.index_u32());
             commands
                 .entity(coin)
                 .insert(VisibleGameEntity)

src/entities/item/systems.rs

@@ -116,13 +116,13 @@ pub fn item_tile_management_system(
 
         for position in positions {
             let items = match tilemap.item_tiles.get(&position) {
-                Some(i) => i,
+                Some(i) => i.clone(),
                 None => continue,
             };
 
             // Clean up empty tiles
             if items.is_empty() {
-                tilemap.item_tiles.remove(&position);
+                tilemap.remove_item(&position);
                 rotation_timer.current_indices.remove(&position);
                 continue;
             }
@@ -146,8 +146,8 @@ pub fn item_tile_management_system(
                 .copied()
                 .unwrap_or(0);
 
-            for &entity_id in items {
-                if let Some(entity) = Entity::from_raw_u32(entity_id) {
+            for entity_id in &items {
+                if let Some(entity) = Entity::from_raw_u32(*entity_id) {
                     if let Ok(mut rotation_state) = item_query.get_mut(entity) {
                         rotation_state.should_be_visible = false;
                     }