[DOC] 1.0 Migration Guide

[henrydingliu]

Do not merge till all warnings are actually live in the library

Summary of Changes

new page that details all breaking changes and deprecations for 1.0

Related GitHub Issue(s)

AI/LLM Usage

None

Additional Context for Reviewers

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

Low Risk
Documentation and TOC only; no runtime or API code changes in this diff.

Overview
Adds a Chainladder 1.0 migration guide to the Jupyter Book and wires it into the table of contents as a new library/migration_guide.md chapter (between the user guide and Friedland material).

The new page catalogs upcoming [BRK] items for 1.0 (Dask/Cupy removal, Triangle.astype no inplace, == vs equals, PTF_Formula → ptf_formula) and [DEPR] notices for later releases (development → valuation/age, Sparse backend, inplace=True return value, slice indexing on Triangle.at), with rationale and migration snippets where applicable.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.14%. Comparing base (d046ca3) to head (3acc3ba).

Additional details and impacted files

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  Files          96       96           
  Lines        5843     5843           
  Branches      739      739           
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  Hits         5501     5501           
  Misses        221      221           
  Partials      121      121           

Flag	Coverage Δ
unittests	94.14% <ø> (ø)

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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): 15.6% of exported symbols fully typed (227 / 1456)

	Known	Ambiguous	Unknown	Total
Project (head)	227	108	1121	1456

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: 326
• Functions without default param: 0
• Classes without docstring: 8

Patch (exported symbols added or changed by this PR): no exported symbol type-completeness changes detected.