feat: settle net roll-aware return

[XucroYuri]

episode 摘要增加扣减 T+1 settle gap 后的真实换月净收益。

[Copilot]

🟡 Changes recommended

The new settle-net summary metrics are not validated by tests beyond non-null checks, leaving key behavior insufficiently protected against regressions.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR extends the episode return summary produced by contract_episode_return_summary() to include a “settle” (T+1 settle gap adjusted) net roll-aware return, aligning the episode摘要 with the requested “扣减 T+1 settle gap 后的真实换月净收益” reporting.

Changes:

• Add per-episode settle_net_roll_aware_return computed as roll_aware_return - t1_settle_gap.
• Add aggregate summary metrics for the new settle-net series (valid count + mean).
• Document the new output in CHANGELOG.md and mark it completed in .planning/ROADMAP.md.

File summaries

File	Description
tests/test_contracts.py	Adds a presence check for the new per-row settle_net_roll_aware_return field.
src/goratio/contracts.py	Computes settle-net roll-aware return per row and adds aggregate count/mean fields.
CHANGELOG.md	Notes the new settle-net episode summary output.
.planning/ROADMAP.md	Marks open/settle dual net-return output as completed.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Lite

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