Improve insertion_sort docstring with complexity analysis (#14875)

* Improve insertion_sort docstring with complexity analysis

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Fix doctest formatting

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Apply suggestion from @cclauss

---------

Co-authored-by: Shreya <youremail@example.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

Author: 4 people

sorts/pancake_sort.py

@@ -25,6 +25,9 @@ def pancake_sort[T](arr: Sequence[T]) -> list[T]:
     []
     >>> pancake_sort([-2, -5, -45])
     [-45, -5, -2]
+
+    Time Complexity: (O(n^2))
+    Space Complexity: (O(n))
     """
     cur = len(arr)
     while cur > 1:
@@ -39,6 +42,9 @@ def pancake_sort[T](arr: Sequence[T]) -> list[T]:
 
 
 if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
     user_input = input("Enter numbers separated by a comma:\n").strip()
     unsorted = [int(item) for item in user_input.split(",")]
-    print(pancake_sort(unsorted))
+    print(f"{pancake_sort(unsorted) = }")