Use smoothing=0 in audeer.progress_bar()

[hagenw]

Closes audeering/audb#442

This makes the estimation of the remaining time in the progress bar less eratic.

For a single thread it changed the behavior from

to

And when using 4 threads it changes the behavior from

to

[ChristianGeng]

This is an exponential smoothing parameter. Setting it to 0 afaics seems to result in a mean estimate of all previous iteration durations.

This is safe and can be approved.

[hagenw]

This is safe and can be approved.

It's always complicated with judging all the effects a setting on the progress bar has. Sometimes you realize only after a few days of using it, that it has some unwanted consequences. But the good news is, it will not result in any failing code ;)

If we really find a strange side effect of this, we can revert the change in a later release.