Update type annotation in get_finite_datetime_ranges_from_timestamps

Before this change, the finite_datetime_range argument to this
function had the type FiniteDatetimeRange.

The function doesn't use any of the methods from that class and works
when called on objects of its parent type
FiniteRange[datetime.datetime], so this change updates the type
annotation to reflect that.

xocto/ranges.py

@@ -794,7 +794,7 @@ def days(self) -> int:
 
 
 def get_finite_datetime_ranges_from_timestamps(
-    finite_datetime_range: FiniteDatetimeRange,
+    finite_datetime_range: FiniteRange[datetime.datetime],
     timestamps: list[datetime.datetime],
 ) -> Sequence[FiniteDatetimeRange]:
     """