Write a Python program to remove duplicates from a list.
Implement remove_duplicates(items) so it returns a new list containing each value only once, preserving the order of its first occurrence. The input list contains hashable values, and the original list must not be modified.
Examples:
[3, 1, 3, 2, 1] returns [3, 1, 2].[] returns [].Constraints: 0 <= len(items) <= 10^4.
def remove_duplicates(items):