message: Add train_round method to participant
diff: -from typing import List, Tuple
  +from typing import Any, List, Tuple
  import numpy as np
  import tensorflow as tf
  @@ -26,8 +26,13 @@ class Participant:
  self.steps_train = int(xy_train[0].shape[0] / BATCH_SIZE)
  self.steps_val = int(xy_val[0].shape[0] / BATCH_SIZE)
  - def replace_model(self, model: tf.keras.Model) -> None:
  - self.model = model
  + def train_round(
  + self, theta: List[List[np.ndarray]], epochs
  + ) -> Tuple[List[List[np.ndarray]], Any]:
  + self.update_model_parameters(theta)
  + history = self.train(epochs)
  + theta_prime = self.retrieve_model_parameters()
  + return theta_prime, history
  def update_model_parameters(self, theta: List[List[np.ndarray]]) -> None:
  ops.set_model_params(self.model, theta)
  @@ -35,7 +40,7 @@ class Participant:
  def retrieve_model_parameters(self) -> List[List[np.ndarray]]:
  return ops.get_model_params(self.model)
  - def train(self, epochs: int):
  + def train(self, epochs: int) -> Any:
  history = self.model.fit(
  self.ds_train,
  epochs=epochs,
  @@ -53,6 +58,9 @@ class Participant:
  loss, accuracy = self.model.evaluate(ds_val, steps=1)
  return loss, accuracy
  + def replace_model(self, model: tf.keras.Model) -> None:
  + self.model = model
  +
  def init_participants(xy_splits, xy_val) -> List[Participant]:
  participants = []
  