batch editing option: add delay per edit

[rwst]

The behaviour of the Wikidata API changed, as seen at https://phabricator.wikimedia.org/T256386 I think adding a delay option (multiples of 0.1s) would allow me to avoid failed-saves.

But I could be wrong about it all. What do you think?

[maxlath]

Setting a delay would still allow some requests to fail if the delay becomes too short. My preferred approach would rather be to retry after a delay after having encountered a failed-save, just like when we get a maxlag error: that would allow to adapt to the server capacity without having to guess the appropriate delay.

[maxlath]

I just published v15.15.1, which should do that retry on failed-save; could you test to see if that solves the problem?

[rwst]

This works fine, many thanks! The fail phases usually are shorter than 30s.