input: Write a python function to read a CSV file and return the columns 'x', 'y', 'z' as lists.
  assert read_csv_columns('data/my_dataset.csv') == ([x_values], [y_values], [z_values])
output: def read_csv_columns(file_path):
      import csv
      
      x, y, z = [], [], []
      
      with open(file_path, 'r') as file:
          reader = csv.DictReader(file)
          for row in reader:
              x.append(row['x'])
              y.append(row['y'])
              z.append(row['z'])
      
      return x, y, z