[FEAT] Centralize axis descriptors

[priyam0k]

Summary of Changes

• Centralizes axis order tuples and lookup mappings in utility_functions and re-exports in core.typing.
• Migrates origin and development to TriangleAxis descriptors, retiring separate internal dimension storage into _axes.
• Implements Triangle._set_axis to generalize dimension validation and assignment.
• Adds TrianglePandas._get_axis_number and routes _get_axis to eliminate redundant local lookup dicts.
• Adds comprehensive unit tests for _set_axis and legacy pickle unpickling.

Related GitHub Issue(s)

Closes #1053

AI/LLM Usage

Used basic model for initial unit test drafting and lint checks.

Additional Context for Reviewers

Follow-up to Issue #1053, stacked directly on top of #1304 (Stack #1437). Can be reviewed here and retargeted to main once Stack #1437 finishes merging.

Submitter's Checklist

• I have reviewed and am adhering to the standards outlined in the project Governing Doc.
• The PR subject title summarizes the changes, with one proper prefix ([FIX], [FEAT], [DOCS], [TST], [CHORE], or [BRK]).
• I am a human (not a bot), and this PR form is written by a human.

Reviewer's Checklist

• The implementation addresses the associated issue(s).
• The implementation is appropriate, maintainable, and follows ARCHITECTURE.md.
• PR subject title has the proper prefix and the subject is appropriate.
• Relevant issue(s) are linked.
• AI/LLM usage is disclosed and appropriate.
• Documentation and tests are appropriate.
• CI tests passed, or any failures are acceptable.
• Leave a comment with the final recommendation (e.g. approve as is, request a secondary review, or flag an area for more review).

---

Note

Medium Risk
Touches core Triangle axis storage, assignment, and unpickling paths; behavior is intended to be preserved but regressions could affect slicing, renaming, and serialized workflows.

Overview
Centralizes Triangle axis handling by moving shared name/number resolution into utility_functions (re-exported from core.typing) and routing TrianglePandas._get_axis_number / TriangleBase._get_axis_value through those helpers instead of local dicts.

Migrates origin and development to TriangleAxis descriptors (like index/columns): getter/setter logic lives in chainladder/core/axis.py, raw timestamps/lags are stored in _axes[2]/_axes[3] via _odims/_ddims setters, and Triangle._set_axis assigns any axis by name or index.

Pickle __setstate__ now normalizes legacy odims/ddims/origin/development keys into _axes and drops redundant state. Tests cover _set_axis, descriptor edge cases (patterns, valuation triangles), and expanded legacy unpickling.

^{Reviewed by Cursor Bugbot for commit deecc2a. 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): 15.6% of exported symbols fully typed (232 / 1488)

	Known	Ambiguous	Unknown	Total
Project (head)	232	108	1148	1488

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: 327
• Functions without default param: 0
• Classes without docstring: 8

Patch (exported symbols added or changed by this PR): 50.0% fully typed (2 / 4)

	Known	Ambiguous	Unknown	Total
Patch	2	0	2	4

Patch symbol details

Symbol	Status	Change
chainladder.core.tests.test_triangle.test_centralized_axis_edge_cases	❌ unknown	new
chainladder.core.tests.test_triangle.test_set_axis	❌ unknown	new
chainladder.core.triangle.Triangle.development	✅ known	changed (was ❌ unknown)
chainladder.core.triangle.Triangle.origin	✅ known	changed (was ❌ unknown)

[codecov]

Codecov Report

❌ Patch coverage is 97.80220% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.12%. Comparing base (5668b6d) to head (deecc2a).

Files with missing lines	Patch %	Lines
chainladder/core/axis.py	94.73%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##           feature/deprecate-date-dims    #1454      +/-   ##
===============================================================
+ Coverage                        94.07%   94.12%   +0.04%     
===============================================================
  Files                               97       97              
  Lines                             5996     6044      +48     
  Branches                           778      790      +12     
===============================================================
+ Hits                              5641     5689      +48     
+ Misses                             227      226       -1     
- Partials                           128      129       +1     

Flag	Coverage Δ
unittests	94.12% <97.80%> (+0.04%)	⬆️

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