ecg_quality(method='averageQRS') is not bounded

[cgastaud]

Describe the bug
In ecg_quality() with method averageQRS, the result is expected to be an array between 0 and 1. However, since after rescaling the signal is interpolated with a quadratic method, this property no longer holds.
This can be easily solved by either choosing a linear interpolation method or clipping the result afterwards.

To Reproduce
ecg = nk.ecg_simulate(duration=10, heart_rate=70, random_state=0)
print(nk.ecg_quality(ecg).min(), nk.ecg_quality(ecg).max())

Expected behaviour
an array between 0 and 1

[welcome]

Hi 👋 Thanks for reaching out and opening your first issue here! We'll try to come back to you as soon as possible. ❤️

[DominiqueMakowski]

That's a good point. I think we could use the same monotonic interpolation that we use for heart rate; or indeed, linear, which probably makes even more sense. Could you consider making a PR to implement the change?