- The `review` phase ends when a MR is merged, not "merged OR closed".
- The `code` phase starts when a MR is first mentioned in a commit, and
  ends when a merge request closing the issue is created.
- The `plan` phase ends when the issue first mentioned in a commit.

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- Fix the `median` function so it sorts the incoming data points.
- A data point where `end_time` is prior to `start_time` is invalid.