template: better prune support in obsfate successorssets don't returns good results for pruned commit, add a workaround for simple cases. A proper fix would require a large rework of successorssets algorithm, I will send a separate series for this refactoring.

template: compute dates in obsfatedate Extract the dates from obsmarkers. Compute the min and max date from the obsmarker range list.

template: compute user in obsfateusers Extract, deduplicate users informations from obs markers in order to display them. Print all users for the moment, we might want to display users only in verbose mode later.