Add index, columns, origin, development alternatives to Triangle.drop()

[priyam0k]

Summary of Changes

Adds index, columns, origin, and development keyword alternatives to Triangle.drop(), mirroring DataFrame.drop().

• each alternative routes to its axis, so columns=... equals labels=..., axis=1, index=... equals axis=0, and so on
• specifying labels together with any alternative raises ValueError, matching pandas
• columns= works today since the column axis is implemented; index, origin, and development route to their axis and still raise NotImplementedError until those axes land in Allow TrianglePandas.drop() to drop index labels #1051, Allow Triangle.drop() to drop origin levels #1055, Allow Triangle.drop() to drop development periods #1057
• added tests for the alternatives, the list form, the conflict error, and the not-yet-implemented axes

Related GitHub Issue(s)

closes #1060, part of #1052

Additional Context for Reviewers

• kept the labels=None with nothing specified path as is, that is handled separately in [BUG] Handle case when labels=None in Triangle.drop() #1062

• no behavior change for the existing labels/axis form

• I passed tests locally for code (pytest)

---

Note

Low Risk
Column-drop behavior for the legacy API is preserved; new kwargs mainly add routing and errors on non-column axes, with coverage in unit tests.

Overview
Triangle.drop() now accepts index, columns, origin, and development as pandas-style shortcuts (e.g. tri.drop(columns='CumPaidLoss') instead of labels=..., axis=1). Mixing labels with any of those kwargs raises ValueError.

Implementation builds a per-axis drop map and normalizes scalars with np.isscalar; only the column axis still drops data—other axes route through the same path and raise NotImplementedError until follow-up work lands. The existing labels/axis API is unchanged.

TriangleProtocol and doctest examples were updated; tests cover equivalence, list/index-like columns, conflicts, and unimplemented axes.

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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): 14.8% of exported symbols fully typed (191 / 1287)

	Known	Ambiguous	Unknown	Total
Project (head)	191	110	986	1287

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: 312
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): 0.0% fully typed (0 / 6)

	Known	Ambiguous	Unknown	Total
Patch	0	0	6	6

Patch symbol details

Symbol	Status	Change
chainladder.core.tests.test_triangle.test_drop_columns_alternative	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_columns_alternative_index_like	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_columns_alternative_list	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_index_origin_development_alternatives_raise	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_integer_label_routes_to_axis	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_labels_and_alternative_raises	❌ unknown	new

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.82%. Comparing base (4533ef6) to head (8157830).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1131      +/-   ##
==========================================
+ Coverage   90.81%   90.82%   +0.01%     
==========================================
  Files          91       91              
  Lines        5300     5308       +8     
  Branches      673      676       +3     
==========================================
+ Hits         4813     4821       +8     
  Misses        346      346              
  Partials      141      141              

Flag	Coverage Δ
unittests	90.82% <100.00%> (+0.01%)	⬆️

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[henrydingliu]

@genedan wanna take this one?

[genedan]

Okay, I'm gonna help knock out the contributing guide draft beforehand. Might take me a day or two? I figured I need to get on it since we keep talking about it.

[genedan]

Finally got around to this, many thanks for the PR. I only have minor comments.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[genedan]

I would recommend adding 1 more print statement showing the original columns of the triangle.