#919 friedland gl self insurer grain

[kennethshsu]

Summary of Changes

Now the valuation date format is explicit

Related GitHub Issue(s)

Fixes #919

Additional Context for Reviewers

N/A

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

---

Note

Low Risk
Localized sample-loader and manifest metadata change; only one bundled dataset gets a new format string, with no auth or core algorithm changes.

Overview
Fixes incorrect development/valuation grain for the friedland_gl_self_insurer sample by wiring optional development_format through the sample manifest into load_sample → Triangle.

The manifest gains an optional development_format field (documented in _manifest.py). Only friedland_gl_self_insurer sets it to %Y-12-31, so calendar-year development columns are parsed as explicit year-end dates instead of being inferred ambiguously. load_sample reads config.get("development_format") and passes it when constructing the triangle.

Minor cleanup in utility_functions: import formatting and a small simplification of date_delta_adjustment (no behavior change intended).

^{Reviewed by Cursor Bugbot for commit 3993b4a. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.28%. Comparing base (8a4f172) to head (3993b4a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #921   +/-   ##
=======================================
  Coverage   88.28%   88.28%           
=======================================
  Files          88       88           
  Lines        5028     5029    +1     
  Branches      642      642           
=======================================
+ Hits         4439     4440    +1     
  Misses        444      444           
  Partials      145      145           

Flag	Coverage Δ
unittests	88.28% <100.00%> (+<0.01%)	⬆️

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[henrydingliu]

someone's linter at it again

[kennethshsu]

Man I hate this... We basically have a competing linter...

[kennethshsu]

@genedan @henrydingliu what linter are you using? Can we just use the same one? x.x

Are you all on ruff?

[henrydingliu]

black. but i rarely turn it on

[kennethshsu]

I'm using black too, and mine is apply on save lol