Use QuadraticModels and LLSModels

[MaxenceGollier]

@dpo

• Remove R2NModel introduced in JSO Compliance: R2N & R2DH #172 by using QuadraticModels.jl, we should first remove the type instabilities/allocations present in that package
• Remove LMModel introduced in JSO Compliance : LM #200 by using LLSModels.jl, we should add a regularized version of least square models there first

[dpo]

The regularized LLSModel should have an option to not add the term $\tfrac{1}{2} \sigma |s|^2$ to the objective value. We don't need that term when we compute $\xi$.