[Feature] Add signal_flatintervals function for flatline detection

[jchromik]

Description

This PR aims at adding the function signal_flatintervals. The function can identify flatline intervals in signals and if modelled after signal_flatline. We discussed this feature in #823. It is one step towards making NeuroKit able to process long-term ECGs with bad or unprocessable intervals.

Possible Next Step

A possible next step could be to a bad_intervals keyword argument to the peak detection functions to that the peak detector does not need to process the whole signal but only the good (non-flatline parts).

Limitations / Concerns

• The function signal_flatintervals needs two "magic" parameters threshold and tolerance. threshold is the same as in signal_flatline with a default values of 0.01 (1% percent of the largest spike in the signal). tolerance says how long the flatline interval needs to be to be recognised as such default is 60 seconds.
• The test uses ecg_simulate and is therefore quite slow (approx. 10s). I am open to suggestions on how to speed this up.

Checklist

• [x] I have read the CONTRIBUTING file.
• [x] My PR is targeted at the dev branch (and not towards the master branch).
• [x] I ran the CODE CHECKS on the files I added or modified and fixed the errors. --> I did not correct complains in code that I did not touch
• [x] I have added the newly added features to News.rst (if applicable) --> not applicable

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (87c8c60) 54.82% compared to head (59d0c83) 54.88%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #940 +/- ## ========================================== + Coverage 54.82% 54.88% +0.05% ========================================== Files 304 305 +1 Lines 14269 14287 +18 ========================================== + Hits 7823 7841 +18 Misses 6446 6446 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[jchromik]

@DominiqueMakowski I renamed the parameter tolerance to duration_min. All checks pass now. Code cov is complete for all my changes. (I'm still open for feedback and critique, though ;-) )

[stale[bot]]

Is this still relevant? If so, what is blocking it? Is there anything you can do to help move it forward?

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.