Improve get_times function to slice timestamps

[alejoe91]

This is needed for chronic data, since times can't fit in memory....

[samuelgarcia]

cool

[chrishalcrow]

Looks good. Widgets all working for me locally.

[h-mayorquin]

LGTM

The path of slicing a time vector with args is not covered:

def test_get_times_with_time_vector_slicing():
    sampling_frequency = 10_000.0
    recording = generate_recording(durations=[1.0], num_channels=3, sampling_frequency=sampling_frequency)
    times = 1.0 + np.arange(0, 10_000) / sampling_frequency
    recording.set_times(times=times, segment_index=0, with_warning=False)

    # Full get_times should return the complete time vector
    times_full = recording.get_times(segment_index=0)
    assert np.allclose(times_full, times)

    # Sliced get_times should match slicing the full vector
    times_slice = recording.get_times(segment_index=0, start_frame=1000, end_frame=8000)
    assert np.allclose(times_slice, times[1000:8000])

    # Only start_frame provided
    times_from_start = recording.get_times(segment_index=0, start_frame=5000)
    assert np.allclose(times_from_start, times[5000:])

    # Only end_frame provided
    times_to_end = recording.get_times(segment_index=0, end_frame=3000)
    assert np.allclose(times_to_end, times[:3000])