TEST: Add tests for base.py

[genedan]

Summary of Changes

Addresses uncovered lines in base.py. I left out tests for anything dealing with dask or cupy.

Related GitHub Issue(s)

Additional Context for Reviewers

• 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
Changes are almost entirely tests plus minor type hints and a dependency lock constraint; no production logic changes beyond annotations.

Overview
Adds pytest coverage for TriangleBase behaviors that were previously untested (dask/cupy paths excluded per PR notes).

New tests lock in input sanitization (rows with development before origin trigger a warning and are dropped), _auto_sparse() (no-op when AUTO_SPARSE is off; numpy→sparse when size/density thresholds are met), subtriangles, NumPy __array__ / __array_function__ dispatch (including TypeError for unhandled or mixed types), and DataFrame interchange construction via a Polars frame.

base.py only gains typing polish: _auto_sparse is annotated to return Triangle, and a TYPE_CHECKING import for Triangle.

uv.lock caps pandas at <=3.0.3 alongside the existing >=2.3.3 lower bound.

^{Reviewed by Cursor Bugbot for commit 8651777. 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): 14.7% of exported symbols fully typed (184 / 1252)

	Known	Ambiguous	Unknown	Total
Project (head)	184	106	962	1252

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: 313
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): 25.0% fully typed (2 / 8)

	Known	Ambiguous	Unknown	Total
Patch	2	0	6	8

Patch symbol details

Symbol	Status	Change
chainladder.core.tests.test_triangle.test_array_dunder	❌ unknown	new
chainladder.core.tests.test_triangle.test_array_function_mixed_types_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_array_function_unhandled_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_auto_sparse_converts_numpy_to_sparse	❌ unknown	new
chainladder.core.tests.test_triangle.test_auto_sparse_disabled_returns_self	❌ unknown	new
chainladder.core.tests.test_triangle.test_development_before_origin_warns_and_drops	✅ known	new
chainladder.core.tests.test_triangle.test_subtriangles	❌ unknown	new
chainladder.core.tests.test_triangle.test_triangle_from_dataframe_interchange_protocol	✅ known	new

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.06%. Comparing base (7d512f1) to head (8651777).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1083      +/-   ##
==========================================
+ Coverage   89.74%   90.06%   +0.32%     
==========================================
  Files          91       91              
  Lines        5287     5287              
  Branches      671      671              
==========================================
+ Hits         4745     4762      +17     
+ Misses        381      370      -11     
+ Partials      161      155       -6     

Flag	Coverage Δ
unittests	90.06% <100.00%> (+0.32%)	⬆️

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