Train/test split, k-fold cross-validation, bootstrapping

Implement:

def train_test_split(input, labels, test_size, seed=None) -> tuple[np.ndarray, np.ndarray, np.ndarray, np.ndarray]: ...
def k_fold_split(n_samples, k, seed=None) -> list[tuple[np.ndarray, np.ndarray]]: ...

• Bootstrapping itself is already implemented, 02-bagging's bootstrap_sample, reuse it, this question doesn't reimplement it.