Preserve Duration state in pickle and shallow copies

src/pendulum/duration.py

@@ -15,6 +15,8 @@
 
 
 if TYPE_CHECKING:
+    from typing import SupportsIndex
+
     from typing_extensions import Self
 
 
@@ -470,6 +472,9 @@ def __deepcopy__(self, _: dict[int, Self]) -> Self:
             weeks=self.weeks,
         )
 
+    def __reduce_ex__(self, protocol: SupportsIndex) -> tuple[object, ...]:
+        return (*super().__reduce_ex__(protocol), self.__dict__)
+
 
 Duration.min = Duration(days=-999999999)
 Duration.max = Duration(

tests/duration/test_behavior.py

@@ -2,6 +2,7 @@
 
 import pickle
 
+from copy import copy
 from copy import deepcopy
 from datetime import timedelta
 
@@ -20,6 +21,37 @@ def test_pickle() -> None:
     assert it == it2
 
 
+@pytest.mark.parametrize("protocol", range(pickle.HIGHEST_PROTOCOL + 1))
+@pytest.mark.parametrize("years, months", [(2, 3), (-2, -3), (1, -2)])
+def test_pickle_preserves_calendar_components(
+    protocol: int, years: int, months: int
+) -> None:
+    original = pendulum.duration(
+        years=years, months=months, weeks=1, days=2, seconds=37, microseconds=123
+    )
+    restored = pickle.loads(pickle.dumps(original, protocol=protocol))
+
+    assert restored == original
+    assert restored.years == original.years
+    assert restored.months == original.months
+    assert restored.weeks == original.weeks
+    assert restored.remaining_days == original.remaining_days
+    assert restored.seconds == original.seconds
+    assert restored.microseconds == original.microseconds
+    assert str(restored) == str(original)
+
+
+def test_shallow_copy_preserves_calendar_components() -> None:
+    original = pendulum.duration(years=1, months=2, days=9)
+    copied = copy(original)
+
+    assert copied is not original
+    assert copied == original
+    assert copied.years == original.years
+    assert copied.months == original.months
+    assert str(copied) == str(original)
+
+
 def test_comparison_to_timedelta() -> None:
     duration = pendulum.duration(days=3)