fix(capecod): include on-level factor in exposure weighting (#1308, #1319)

[priyam0k]

Summary of Changes

• Included sample weight on-level factors in the Cape Cod weighted exposure calculation so premium rate changes are properly reflected in the a priori loss ratio.
• Updated Friedland Chapter 10 Exhibit II to use native CapeCod on-level functionality directly in the pipeline instead of manual pandas steps.
• Fixed notebook lint issues in Chapter 10 and removed its grandfathered ignore entry from pyproject.toml.
• Added a unit test validating Cape Cod with both rate level changes and tort reform against textbook values.

Related GitHub Issue(s)

• Fixes [BUG] Potential Bug in Capecod #1308
• Closes [REFACTOR] Friedland Chapter 10 CapeCod on-leveling and add tests #1319
• Helps with Initial Linting Cleanup #1216

Additional Context for Reviewers

All pre-commit ruff checks and tests pass cleanly.

Checklist

• I passed tests locally for both code (uv run pytest) and documentation changes (uv run --directory docs jb build . --builder=custom --custom-builder=doctest)

---

Note

Medium Risk
Changes core Cape Cod apriori math for any fit with on-leveled sample_weight, which directly shifts derived loss ratios and ultimates; scope is narrow and guarded by new textbook reconciliation tests.

Overview
Cape Cod now multiplies used-up exposure by the sample-weight on-level factor (sw_olf_array) when building weighted_exposure for the all-years apriori, so rate-level adjustments on earned premium affect the weighted loss ratio the same way they already did in the loss numerator.

A regression test reproduces Friedland Chapter 10 Exhibit II (rate parallelogram on premium, tort OLF on losses, floored development, trend) and checks apriori, detrended_apriori_, and total ultimate. The Chapter 10 notebook is updated to drive Exhibit II through a Pipeline and model outputs (detrended_apriori_, expectation_, ibnr_, ultimate_) instead of hand-rolled detrending; minor formatting fixes allow dropping the notebook’s ruff grandfather entry in pyproject.toml.

^{Reviewed by Cursor Bugbot for commit a98795e. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Pyright Type Completeness

View the full pyright --verifytypes output for this commit

Project (full chainladder package, at this PR's head): 15.1% of exported symbols fully typed (208 / 1381)

	Known	Ambiguous	Unknown	Total
Project (head)	208	111	1062	1381

Other symbols referenced but not exported by chainladder: 13

	Known	Ambiguous	Unknown	Total
Other (head)	3	1	9	13

Symbols without documentation:

• Functions without docstring: 327
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): 0.0% fully typed (0 / 1)

	Known	Ambiguous	Unknown	Total
Patch	0	0	1	1

Patch symbol details

Symbol	Status	Change
chainladder.methods.tests.test_capecod.test_capecod_onlevel_friedland_exhibit_ii	❌ unknown	new

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.79%. Comparing base (d7479a4) to head (a98795e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1339      +/-   ##
==========================================
+ Coverage   91.76%   91.79%   +0.03%     
==========================================
  Files          96       96              
  Lines        5475     5475              
  Branches      706      706              
==========================================
+ Hits         5024     5026       +2     
+ Misses        327      326       -1     
+ Partials      124      123       -1     

Flag	Coverage Δ
unittests	91.79% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[henrydingliu]

try Triangle.maximum