fix: start Community Prediction at question open_time

[SylvainChevalier]

Pre-predictions made before the question opens were being included in the CP timeline, causing it to start before open_time. Now clip pre-open forecasts so the CP timeline begins at the question's open_time, while still incorporating the most recent pre-open forecast state from each user that is still active at open_time.

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[SylvainChevalier]

@lsabor feel free to throw away if bad.

[github-actions]

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• Commit: 44ca9693ee77fb450510deb47d43477076b4ea9a
• Branch: claude/issue-4684-community-prediction-should-start-at
• Fly App: metaculus-pr-4688-claude-issue-4684-community-pr

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[SylvainChevalier]

@claude please fix the issues revealed by the unit tests.

[claude]

Claude finished @SylvainChevalier's task in 5m 38s —— View job

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CI fix pushed

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Summary

The "unit tests" CI run was failing only because of the Check Ruff formatting step in the Backend Checks job — all 712 unit tests passed. The offender was utils/the_math/aggregations.py:

Would reformat: utils/the_math/aggregations.py
1 file would be reformatted, 306 files already formatted

The two new if (...) blocks added in this PR were written as multi-line:

if (
    earliest_time
    and forecast.end_time
    and forecast.end_time <= earliest_time
):

Once collapsed they fit on a single 86-char line (under the project's 88 limit), which is the form ruff/Black enforce. Both occurrences (in get_user_forecast_history) were collapsed in commit 9064059.

Note: I couldn't install ruff in this sandbox (no network), so I couldn't run ruff format directly. The fix is based on analysis of ruff's Black-compatible behavior and the project's line-length = 88. CI will verify on the next run.
• Branch: claude/issue-4684-community-prediction-should-start-at