[BE] wrap deprecated function/class with typing_extensions.deprecated (#126898)

Use `typing_extensions.deprecated` for deprecation annotation if possible. Otherwise, add `category=FutureWarning` to `warnings.warn("message")` if the category is missing.

Note that only warnings that their messages contain `[Dd]eprecat(ed|ion)` are updated in this PR.

UPDATE: Use `FutureWarning` instead of `DeprecationWarning`.

Resolves #126888

- #126888

Pull Request resolved: https://github.com/pytorch/pytorch/pull/126898
Approved by: https://github.com/albanD

torch/hub.py

@@ -13,6 +13,7 @@ import warnings
 import zipfile
 from pathlib import Path
 from typing import Dict, Optional, Any
+from typing_extensions import deprecated
 from urllib.error import HTTPError, URLError
 from urllib.request import urlopen, Request
 from urllib.parse import urlparse  # noqa: F401
@@ -680,10 +681,13 @@ def _is_legacy_zip_format(filename: str) -> bool:
     return False
 
 
+@deprecated(
+    'Falling back to the old format < 1.6. This support will be '
+    'deprecated in favor of default zipfile format introduced in 1.6. '
+    'Please redo torch.save() to save it in the new zipfile format.',
+    category=FutureWarning,
+)
 def _legacy_zip_load(filename: str, model_dir: str, map_location: MAP_LOCATION, weights_only: bool) -> Dict[str, Any]:
-    warnings.warn('Falling back to the old format < 1.6. This support will be '
-                  'deprecated in favor of default zipfile format introduced in 1.6. '
-                  'Please redo torch.save() to save it in the new zipfile format.')
     # Note: extractall() defaults to overwrite file if exists. No need to clean up beforehand.
     #       We deliberately don't handle tarfile here since our legacy serialization format was in tar.
     #       E.g. resnet18-5c106cde.pth which is widely used.