input: Write a python function to detect duplicates in a CSV file.
  assert find_duplicates("test1.csv") == {('John', 'Doe', '35'), ('Jane', 'Smith', '28')}
  assert find_duplicates("test2.csv") == set()
  assert find_duplicates("test3.csv") == {('Alice', 'Wonderland', '30'), ('Bob', 'Builder', '40')}
output: def find_duplicates(filename):
      import csv
      from collections import defaultdict
  
      rows = []
      duplicates = set()
      seen = set()
  
      with open(filename, newline='') as csvfile:
          reader = csv.reader(csvfile)
          for row in reader:
              row_tuple = tuple(row)
              if row_tuple in seen:
                  duplicates.add(row_tuple)
              else:
                  seen.add(row_tuple)
      return duplicates