Deprecate split_by_epochs and other similar functions

[bburan]

These functions use NaN masks rather than tiled subsets. The problem with NaN values is that it requires the signal to be converted to a floating-point array (rather than preserving the original dtype if it is integer, boolean, etc.). Now that we are using select_times, these functions should be deprecated (or updated to use select_times under the hood.

[bburan]

Sample code for doing the split using select times while preserving the function signature for split_by_epochs:

def split_est_val_by_sequence(recording):
    epochs = recording.epochs
    m = epochs['name'].str.match('^SEQUENCE_')
    sequences = recording.epochs.loc[m, 'name'].unique()
    np.random.shuffle(sequences)
    val_size = round(len(sequences) * 0.2)
    val_epochs, est_epochs = sequences[:val_size], sequences[val_size:]
    m = epochs['name'].apply(lambda x: x in val_epochs)
    val_times = epochs.loc[m][['start', 'end']].values
    m = epochs['name'].apply(lambda x: x in est_epochs)
    est_times = epochs.loc[m][['start', 'end']].values
    val = recording.select_times(val_times)
    est = recording.select_times(est_times)
    return est, val