Refactor helpers.py: move functions to their respective modules

- Move scanner-only functions to scanner.py
- Move query-only functions (is_scalar, project_kv) to asset_info.py
- Move get_query_dict to routes.py
- Create path_utils.py service for path-related functions
- Reduce helpers.py to shared utilities only

Amp-Thread-ID: https://ampcode.com/threads/T-019c2510-33fa-7199-ae4b-bc31102277a7
Co-authored-by: Amp <amp@ampcode.com>

app/assets/manager.py

@@ -26,9 +26,9 @@ from app.assets.database.queries import (
     list_cache_states_by_asset_id,
     touch_asset_info_by_id,
 )
-from app.assets.helpers import (
+from app.assets.helpers import pick_best_live_path
+from app.assets.services.path_utils import (
     ensure_within_base,
-    pick_best_live_path,
     resolve_destination_from_tags,
 )
 from app.assets.services import (