sorted_list_difference failed to deduplicate remaining elements when onelist was exhausted, causing duplicate values in the result.Fix uses dict.fromkeys() to deduplicate before extending.sim:https://taskei.amazon.dev/tasks/TODO

…icationExercise the except-IndexError path where one list is exhaustedand the remaining tail of the other list contains duplicates.These cases were previously untested and would have passed evenwithout the fix in the preceding commit.

Sphinx cannot resolve :func: references to unittest.util since it isnot part of the public documented API. Use double backticks instead.

dict.fromkeys requires hashable elements, which narrows the inputcontract. Replace with a simple consecutive-duplicate removal thatonly uses equality comparison, matching the main loop's approach.Add test cases for strings and unhashable types (lists).