code: def plot_leverages(self):
          
          plt.figure()
          lev = self.leverages()
          plt.xlabel('Sample Index')
          plt.ylabel('Leverage')
          plt.bar(left=range(lev.size), height=lev)
          plt.hlines(y=1/lev.size, xmin=0, xmax=lev.size, colors='r', linestyles='--')
          plt.show()
          return None
docs: Leverage (h) per observation, with a red line plotted at y = 1/Number of samples (expected
          :return: Plot with observation leverages (h)