ci.eval.compare: require the directories to exist (they always should)

    before_stats = Path(options.before)

    after_stats = Path(options.after)

    # This may happen if the pull request target does not include PR#399720 yet.

    if not before_stats.exists():

        print(

            "⚠️  Skipping comparison: stats directory is missing in the target commit."

        )

        exit(0)

    # This should never happen, but we're exiting gracefully anyways

    if not after_stats.exists():

        print(

            "⚠️  Skipping comparison: stats directory missing in current PR evaluation."

        )

        exit(0)

    before_metrics = load_all_metrics(before_stats)

    after_metrics = load_all_metrics(after_stats)

    df1 = perform_pairwise_tests(before_metrics, after_metrics)