Write a function named union_sets that accepts as a parameter a set of sets of integers, and returns a set of integers representing the union of all of the sets of ints.
(A union is the combination of everything in each set.)
For example, calling your function on the following set of sets:
{{1, 3}, {2, 3, 4, 5}, {3, 5, 6, 7}, {42}}
Should cause the following set of integers to be returned:
{1, 2, 3, 4, 5, 6, 7, 42}
(The inner sets in our test cases are actually instances of type frozenset, an immutable set type that can be nested within other set structures.)
