[FIX] Apply Ruff fixes to berqsherm.py.

[genedan]

Summary of Changes

Knocking out chainladder/adjustments/berqsherm.py from the Ruff list. Yeah...we got a long way to go. I tried getting started on bootstrap.py but stopped when the linter was uncovering bugs.

Related GitHub Issue(s)

#1216

Additional Context for Reviewers

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

Low Risk
Lint-only edits to Berquist–Sherman adjustment code with no intended behavioral change.

Overview
Brings chainladder/adjustments/berqsherm.py into compliance with the project Ruff rules so it no longer needs a per-file ignore entry in pyproject.toml.

Changes are formatting and docstring style only: operator spacing in the exponential regression denominator, whitespace in np.clip, and clearer line breaks around the nested xp.concatenate batching for a and b. The transform docstring is normalized to a standard multi-line form (no logic change in fit or transform).

^{Reviewed by Cursor Bugbot for commit 660ab7e. 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): 15.4% of exported symbols fully typed (213 / 1381)

	Known	Ambiguous	Unknown	Total
Project (head)	213	111	1057	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: 325
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): no exported symbol type-completeness changes detected.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.68%. Comparing base (5b79e32) to head (660ab7e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1278   +/-   ##
=======================================
  Coverage   91.68%   91.68%           
=======================================
  Files          93       93           
  Lines        5447     5447           
  Branches      704      704           
=======================================
  Hits         4994     4994           
  Misses        328      328           
  Partials      125      125           

Flag	Coverage Δ
unittests	91.68% <100.00%> (ø)

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