input: Write a python function to calculate the Exponentially Weighted Moving Average (EWMA) of a list of stock prices.
  assert calculate_ewma([5, 10, 20, 25, 10, 8, 22], 0.9) == [5.0, 9.5, 18.05, 23.405, 13.0645, 9.70645, 20.930645]
  assert calculate_ewma([1, 2, 3, 4, 5], 0.8) == [1.0, 1.2, 1.56, 2.048, 2.6384]
  assert calculate_ewma([10, 20, 30], 0.7) == [10.0, 13.0, 20.1]
output: def calculate_ewma(prices, alpha):
      ewma = [prices[0]]
      for price in prices[1:]:
          ewma.append(alpha * price + (1 - alpha) * ewma[-1])
      return ewma