Fix handling of the fold attribute when deep copying DateTime objects

Fixes #767

src/pendulum/datetime.py

@@ -1357,17 +1357,32 @@ def _getstate(
     def __reduce__(
         self,
     ) -> tuple[
-        type[Self], tuple[int, int, int, int, int, int, int, datetime.tzinfo | None]
+        type[Self],
+        tuple[int, int, int, int, int, int, int, datetime.tzinfo | None],
     ]:
         return self.__reduce_ex__(2)
 
     def __reduce_ex__(
         self, protocol: SupportsIndex
     ) -> tuple[
-        type[Self], tuple[int, int, int, int, int, int, int, datetime.tzinfo | None]
+        type[Self],
+        tuple[int, int, int, int, int, int, int, datetime.tzinfo | None],
     ]:
         return self.__class__, self._getstate(protocol)
 
+    def __deepcopy__(self, _: dict[int, Self]) -> Self:
+        return self.__class__(
+            self.year,
+            self.month,
+            self.day,
+            self.hour,
+            self.minute,
+            self.second,
+            self.microsecond,
+            tzinfo=self.tz,
+            fold=self.fold,
+        )
+
     def _cmp(self, other: datetime.datetime, **kwargs: Any) -> int:
         # Fix for pypy which compares using this method
         # which would lead to infinite recursion if we didn't override

tests/datetime/test_behavior.py

@@ -158,6 +158,14 @@ def test_deepcopy():
     assert dt == deepcopy(dt)
 
 
+def test_deepcopy_on_transition():
+    dt = pendulum.datetime(2023, 11, 5, 1, 0, 0, tz="US/Pacific")
+    clone = deepcopy(dt)
+
+    assert dt == clone
+    assert dt.offset == clone.offset
+
+
 def test_pickle_timezone():
     dt1 = pendulum.timezone("Europe/Amsterdam")
     s = pickle.dumps(dt1)