Add HRV to statistics panel

[JanCBrammer]

No description provided.

[chandlermassey4]

It would be useful to add an option to generate a list of HRV features under the statistics tab, or create a new features tab. An option could be added to export this list of features as a '.csv' file.

It is very easy to generate these features from the peaks file which is already included in the GUI by using neurokit2.

# Read the peaks file
df = pd.read_csv(input_file)
rpeaks = df['peaks'].values

# Convert R peak times to sample indices
sampling_rate =250
rpeaks_indices = (rpeaks * sampling_rate).astype(int)

# Generate HRV values
hrv = nk.hrv(rpeaks_indices, sampling_rate=sampling_rate, show=True)

The main goal for many users is often to use the peak intervals to generate HRV features, so this would make the process more efficient.