Sparse fixes

[henrydingliu]

Summary of Changes

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)

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Note

Medium Risk
Changes core Triangle value storage and column assignment on the sparse path, which affects numerical workflows on large sparse triangles; risk is mitigated by expanded tests and explicit errors for unsupported in-place mutation.

Overview
Improves sparse-backed Triangle behavior: numpy interoperability, column assignment, and clearer errors when mutating sparse storage directly.

Triangle.__array__ now returns a dense ndarray for sparse triangles (values.todense()), so np.asarray(triangle) works without exposing raw COO arrays.

Sparse column reassignment (triangle[col] = value) no longer rebuilds via drop(key); it filters the target column out of the existing COO coordinates and merges new data, and accepts raw COO arrays as well as Triangle values. Misaligned new-column concatenation also catches AssertionError.

COO __setitem__ is overridden to raise TypeError with guidance to use the numpy backend for in-place slice assignment on triangle.values.

CI: pytest workflow adds concurrency with cancel-in-progress for duplicate runs on the same ref.

Tests are updated to branch on backend (sparse vs numpy) instead of assuming numpy-only fixtures.

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[github-actions]

Pyright Type Completeness

View the full pyright --verifytypes output for this commit

Project (full chainladder package, at this PR's head): 14.9% of exported symbols fully typed (194 / 1300)

	Known	Ambiguous	Unknown	Total
Project (head)	194	110	996	1300

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: 314
• 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.