Fix Ruff F811: remove duplicate random import

Remove redundant 'import random' on line 683 that was already
imported on line 657 in the performance_comparison function

Author: Prigoistic

data_structures/binary_tree/splay_tree.py

@@ -680,8 +680,6 @@ def performance_comparison() -> None:
     print(f"Root after repeated access to 50: {tree.get_root_key()}\n")
 
     # Random access pattern
-    import random
-
     print("Random access pattern...")
     random.seed(42)
     keys = [random.randint(1, 100) for _ in range(100)]