refactor(v2): isolate legacy provider stack and prune obsolete tests

apps/ingestion/services/__init__.py

@@ -1,9 +1,14 @@
+from django.conf import settings
+
 from .runs import finish_ingestion_run, log_ingestion_error, start_ingestion_run
-from .sync import run_sync_job
 
 __all__ = [
     "start_ingestion_run",
     "finish_ingestion_run",
     "log_ingestion_error",
-    "run_sync_job",
 ]
+
+if settings.LEGACY_PROVIDER_STACK_ENABLED:
+    from .sync import run_sync_job  # pragma: no cover - legacy provider stack only.
+
+    __all__.append("run_sync_job")