Tamás Hakkel

Move traits to ProximalCore, new functions, RecursiveArrayToolsExt, defer loading OSQP

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This PR is part of the effort to make StructuredOptimization as general as possible (see the PR on OperatorCore: https://github.com/JuliaFirstOrder/ProximalCore.jl/pull/5). Changes: - `PrecomposedSlicedSeparableSum`: function to be used for complex problems...