updated plugin refactor and added FTP and SCP plugins , also hydrusnetwork plugin migration

cmdlet/download_file.py

@@ -980,10 +980,14 @@ class Download_File(Cmdlet):
     ) -> Optional[str]:
         if storage is None or not canonical_url:
             return None
+        hydrus_provider = None
         try:
-            from Store.HydrusNetwork import HydrusNetwork
+            registry_helpers = cls._load_provider_registry()
+            get_plugin = registry_helpers.get("get_plugin")
+            if callable(get_plugin):
+                hydrus_provider = get_plugin("hydrusnetwork", {})
         except Exception:
-            HydrusNetwork = None  # type: ignore
+            hydrus_provider = None
 
         try:
             backend_names = list(storage.list_searchable_backends() or [])
@@ -1001,13 +1005,13 @@ class Download_File(Cmdlet):
             except Exception:
                 pass
             try:
-                if HydrusNetwork is not None and isinstance(backend, HydrusNetwork) and not hydrus_available:
+                if hydrus_provider is not None and hydrus_provider.is_backend(backend, str(backend_name)) and not hydrus_available:
                     continue
             except Exception:
                 pass
 
             try:
-                if HydrusNetwork is not None and isinstance(backend, HydrusNetwork):
+                if hydrus_provider is not None and hydrus_provider.is_backend(backend, str(backend_name)):
                     hashes = backend.find_hashes_by_url(canonical_url) or []
                     for existing_hash in hashes:
                         normalized = sh.normalize_hash(existing_hash)