test: add neutralize module tests (11 cases)

[redamancy231-create]

内容

为 features.neutralize 模块补充测试。这是论文复现表中唯一 tests 列为 — 的模块，现在补齐。

测试覆盖（11 个用例）

neutralize_cs（5 个）

• 基本行为：每日期横截面 z-score，均值≈0
• Mask 处理：masked 单元输出为 0
• 常量输入：无截面变异 → 全零
• 边界：单只股票 → 全零
• 边界：全部 masked → 全零

neutralize_industry（6 个）

• 基本行为：行业 OLS 残差，均值≈0
• 附加 log_size 连续回归量
• Mask 处理
• 边界：单只可交易股票
• 边界：完全共线（所有股票同一行业）
• 截面标准差归一化验证

[initial-d]

Reviewed the added neutralization coverage. The cases match the current masked z-score and industry residualization behavior, and all CI jobs pass.

[initial-d]

Thanks for adding the neutralization coverage. I rebuilt the integration history to keep this contribution consistent with the project's pairing workflow:

• preserved the contributor authorship on the test commit
• reconstructed the commit with maintainer attribution and removed the AI-tool co-author trailer
• integrated the contribution through an explicit two-parent merge commit instead of a squash commit
• preserved the exact code tree; this was a history/metadata correction only

The rebuilt contribution commit is 3442a2c, the #33 integration commit is 810ea1e, and the resulting main CI is green on Python 3.9, 3.10, and 3.11.