Use __new__ for datetime.timedelta (#5532)

stdlib/datetime.pyi

@@ -139,8 +139,8 @@ class timedelta(SupportsAbs[timedelta]):
     min: ClassVar[timedelta]
     max: ClassVar[timedelta]
     resolution: ClassVar[timedelta]
-    def __init__(
-        self,
+    def __new__(
+        cls: Type[_S],
         days: float = ...,
         seconds: float = ...,
         microseconds: float = ...,
@@ -148,9 +148,7 @@ class timedelta(SupportsAbs[timedelta]):
         minutes: float = ...,
         hours: float = ...,
         weeks: float = ...,
-        *,
-        fold: int = ...,
-    ) -> None: ...
+    ) -> _S: ...
     @property
     def days(self) -> int: ...
     @property