Refactor lagrangian function

[tmigot]

This would help unify NLS and NLP models for the usual NLP API.

Connected to #111 .

[github-actions[bot]]

Package name	latest	stable
CaNNOLeS.jl
DCISolver.jl
DerivativeFreeSolvers.jl
JSOSolvers.jl
NLPModelsIpopt.jl
OptimizationProblems.jl
Percival.jl
QuadraticModels.jl
SolverBenchmark.jl
SolverTools.jl

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.19 :tada:

Comparison is base (046ec8c) 98.25% compared to head (8955f4d) 98.44%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #113 +/- ## ========================================== + Coverage 98.25% 98.44% +0.19% ========================================== Files 8 8 Lines 976 967 -9 ========================================== - Hits 959 952 -7 + Misses 17 15 -2 ``` | [Impacted Files](https://codecov.io/gh/JuliaSmoothOptimizers/ADNLPModels.jl/pull/113?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers) | Coverage Δ | | |---|---|---| | [src/ADNLPModels.jl](https://codecov.io/gh/JuliaSmoothOptimizers/ADNLPModels.jl/pull/113?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers#diff-c3JjL0FETkxQTW9kZWxzLmps) | `98.18% <100.00%> (+1.12%)` | :arrow_up: | | [src/ad.jl](https://codecov.io/gh/JuliaSmoothOptimizers/ADNLPModels.jl/pull/113?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers#diff-c3JjL2FkLmps) | `97.40% <100.00%> (+1.79%)` | :arrow_up: | | [src/nlp.jl](https://codecov.io/gh/JuliaSmoothOptimizers/ADNLPModels.jl/pull/113?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers#diff-c3JjL25scC5qbA==) | `98.52% <100.00%> (-0.04%)` | :arrow_down: | | [src/nls.jl](https://codecov.io/gh/JuliaSmoothOptimizers/ADNLPModels.jl/pull/113?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers#diff-c3JjL25scy5qbA==) | `98.45% <100.00%> (-0.04%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers)

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