Comment drift fails for pull requests with extremely large diffs

When performing comment drift, the system needs to run certain git diff operations. If the pull request in question is extremely large (whether due to modifying a huge number of files, or due to modifying a number of huge files), these diffs can timeout and trigger comment drift to fail. That results in comment drift stacking up, as well as additional system load due to repeated failures.

Timeout failures in comment drift are not directly user-visible. They only appear in the logs. However, when comment drift is not completing successfully, users may see out-of-place comments in the diff because drift has not been processed.