Rebase commits now created using the merge-ort strategy

Last year, we made merging pull requests much faster by using the merge-ort strategy. Now, rebase commits get the same merge-ort treatment. This results in significantly improved speed: the P99 (the average time to complete rebases excluding the 1% slowest outliers) used to take around 3.6 seconds. P99 with the new strategy is 0.35 seconds. Because of the speedup, the fraction of PR rebases which fail due to timeouts dropped from 1.3% to 0.14%.

Learn more about the Git merge-ort strategy and merge methods for pull requests.