multiple changes at once happen during search and replace operations.

Right now, we are handling each individually, one after another. this breaks starting at the second change because the range of each change is always related to the original state, not the previous. after fiddling with the apply_change method I figured this solution is the easiest. it expects that all changes are ordered properly, but afaik that's reasonable. if not and we receive bug reports, we can simply sort them.

EDIT: ahh I need to handle the deletions case too! ✅