Explore using threads

Python 3.14 (#109 ) supports threads. E-divisive could be trivially multi-threaded such that each time a change point is found and the time series splits into two, both sides could be computed in two separate threads. (Perhaps limited by some maximum amount of total threads.

Update: We decided to continue to support all active python versions. Even so, this could be introduced as an option, and it would default to 1 thread, and on 3.13 and earlier, that would be the only option.