Remove NNMF problem and update Benchmark.jl accordingly

[MohamedLaghdafHABIBOULLAH]

@dpo @MaxenceGollier this should be merged after 249.

[Copilot]

Pull Request Overview

This PR removes the NNMF (Non-Negative Matrix Factorization) problem benchmarking code and cleans up dependencies. The changes eliminate the CFG2 configuration that was specifically used for NNMF benchmarks, remove ProximalOperators/ProximalAlgorithms dependencies in favor of ShiftedProximalOperators, and simplify solver naming in the remaining SVM benchmarks.

• Removes all NNMF-related benchmark functions and workflow
• Updates package dependencies to use ShiftedProximalOperators instead of ProximalOperators
• Simplifies solver naming by removing problem type suffixes

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
paper/examples/example.jl	Updates imports to use ShiftedProximalOperators and adds NLPModelsModifiers
paper/examples/comparison-config.jl	Removes CFG2 configuration that was used for NNMF benchmarks
paper/examples/Project.toml	Removes ProximalOperators, ProximalAlgorithms, and ProximalCore dependencies
paper/examples/Benchmark.jl	Removes all NNMF benchmark functions and simplifies solver naming in SVM benchmarks

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