Remove R2NModels

[MaxenceGollier]

partially solves #220.

[Copilot]

Pull request overview

This PR partially addresses issue #220 by removing the custom R2NModel type and replacing it with QuadraticModel from the QuadraticModels.jl package. The R2NModel was a bespoke NLP model representing the smooth quadratic R2N subproblem; swapping it for QuadraticModel reduces the amount of custom code in the repository and leverages an actively maintained external dependency.

Changes:

• Removes src/R2NModel.jl (the custom model) and its include in RegularizedOptimization.jl
• Replaces R2NModel construction and field access with QuadraticModel and data.H/data.σ in R2N.jl and TR_alg.jl; adds a preallocated work vector v1 to both solver structs
• Adds QuadraticModels as a dependency in Project.toml

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/R2NModel.jl	File deleted — custom quadratic subproblem model removed
src/RegularizedOptimization.jl	Added QuadraticModels to using list; removed include("R2NModel.jl")
src/R2N.jl	Replaces R2NModel with QuadraticModel; updates field accesses to data.H/data.σ; adds v1 work vector; rewrites mk lambda to avoid skip_sigma
src/TR_alg.jl	Same R2NModel → QuadraticModel substitution; adds v1 work vector; updates data.H accesses
Project.toml	Adds QuadraticModels dependency with compat constraint "0.9.15"

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[codecov]

Codecov Report

❌ Patch coverage is 76.19048% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.38%. Comparing base (e0f214d) to head (d251914).
⚠️ Report is 274 commits behind head on master.

Files with missing lines	Patch %	Lines
src/R2N.jl	80.00%	3 Missing ⚠️
src/TR_alg.jl	66.66%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #311       +/-   ##
===========================================
+ Coverage   61.53%   83.38%   +21.85%     
===========================================
  Files          11       12        +1     
  Lines        1292     1643      +351     
===========================================
+ Hits          795     1370      +575     
+ Misses        497      273      -224     

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