[ENH] Accept Series and Triangles in DevelopmentConstant patterns

[priyam0k]

Summary of Changes

Extends cl.DevelopmentConstant to natively accept development patterns in tabular and object formats without requiring manual dictionary conversions:

• pd.Series indexed by development ages or interval strings (e.g., '12-24')
• 1-row or 1-column pd.DataFrame
• 1D cl.Triangle objects (e.g., estimator.ldf_ or estimator.cdf_)
• Fitted estimators exposing ldf_ or cdf_ attributes
• Added unit tests in test_constant.py covering all supported input formats and validation guards.

Related GitHub Issue(s)

Closes #1483

AI/LLM Usage

Used basic model for drafting unit test cases.

Additional Context for Reviewers

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• The implementation addresses the associated issue(s).
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---

Note

Medium Risk
Changes how external development patterns are parsed and mapped to ages; mistakes could skew LDF/CDF outputs, though dict/callable paths are preserved and coverage is broad.

Overview
DevelopmentConstant can take external development patterns as pd.Series, 1-row/1-column DataFrame, single-origin Triangle (e.g. another model’s ldf_ / cdf_), or fitted estimators with those attributes—not only a plain dict or callable.

Non-callable inputs are converted via new _normalize_patterns, which resolves ldf_/cdf_ from estimators per style, parses development ages from labels like 12-24, and rejects invalid shapes (multi-origin triangles, 2D DataFrames, unsupported types). Constructor typing and docs are updated; fit behavior for callables is unchanged.

Tests cover each accepted format, index parsing, estimator fallbacks, and the new validation errors.

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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): 15.9% of exported symbols fully typed (232 / 1461)

	Known	Ambiguous	Unknown	Total
Project (head)	232	106	1123	1461

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: 331
• Functions without default param: 0
• Classes without docstring: 8

Patch (exported symbols added or changed by this PR): 50.0% fully typed (5 / 10)

	Known	Ambiguous	Unknown	Total
Patch	5	0	5	10

Patch symbol details

Symbol	Status	Change
chainladder.development.constant.DevelopmentConstant.__init__	✅ known	changed (was ❌ unknown)
chainladder.development.constant.DevelopmentConstant.callable_axis	✅ known	changed (was ⚠️ ambiguous)
chainladder.development.constant.DevelopmentConstant.groupby	✅ known	changed (was ❌ unknown)
chainladder.development.constant.DevelopmentConstant.patterns	✅ known	changed (was ❌ unknown)
chainladder.development.constant.DevelopmentConstant.style	✅ known	changed (was ⚠️ ambiguous)
chainladder.development.tests.test_constant.test_constant_dataframe_pattern	❌ unknown	new
chainladder.development.tests.test_constant.test_constant_estimator_pattern	❌ unknown	new
chainladder.development.tests.test_constant.test_constant_invalid_pattern_types	❌ unknown	new
chainladder.development.tests.test_constant.test_constant_series_pattern	❌ unknown	new
chainladder.development.tests.test_constant.test_constant_triangle_pattern	❌ unknown	new

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.19%. Comparing base (856f87b) to head (f9fd483).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1484      +/-   ##
==========================================
+ Coverage   94.15%   94.19%   +0.03%     
==========================================
  Files          96       96              
  Lines        5852     5890      +38     
  Branches      739      751      +12     
==========================================
+ Hits         5510     5548      +38     
  Misses        221      221              
  Partials      121      121              

Flag	Coverage Δ
unittests	94.19% <100.00%> (+0.03%)	⬆️

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[henrydingliu]

small nits

[henrydingliu]

this is a neat convenience feature. could you please either document it in the docstring or throw a warning?

[henrydingliu]

a transformed triangle may have ldf_ and wouldn't get here