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
API extension with preserved behavior for labels/axis; column drops use existing selection logic and are covered by new tests.

Overview
Triangle.drop() now accepts index, columns, origin, and development as alternatives to labels + axis, aligned with DataFrame.drop(). For example, drop(columns='CumPaidLoss') matches drop(labels='CumPaidLoss', axis=1). Mixing labels with any of those kwargs raises ValueError.

Implementation builds a per-axis drop map, normalizes scalars with np.isscalar (so integer development labels do not hit the old type(labels) is str bug), and can apply multiple axis kwargs in one call. Only the column axis still performs drops; index, origin, and development route to their axes and raise NotImplementedError until follow-up work lands. The labels/axis API is unchanged.

TriangleProtocol and docs/examples were updated; tests cover equivalence, lists, conflicts, unimplemented axes, and list-like columns inputs.

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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 (65f70d0).
⚠️ 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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