Make Lines iterator more efficient

[cessen]

Currently the Lines iterator is roughly equivalent to just calling Rope::line() repeatedly with an incrementing index. This is O(log N) for each call to Lines::next(), and also is just generally less efficient than it needs to be. This is not only sub-optimal, but also stands out compared to the other iterators which are all O(1) and very fast.

It should be possible to also make Lines O(1) and just generally more efficient.

[poliorcetics]

I was exploring this issue this weekend and I think I have a possible solution, I'll try to post a PR within the month :), it needs lots of polishing and perf testing (thankfully testing for correctness is just comparing to the slow version so that part is easy)

[pascalkuthe]

I was exploring this issue this weekend and I think I have a possible solution, I'll try to post a PR within the month :), it needs lots of polishing and perf testing (thankfully testing for correctness is just comparing to the slow version so that part is easy)

That's a bit unfortunate timing we did some duplicate work here (see my comment in helix-editor/helix#4457). Perhaphs we can combinme efforts