Fix UnsupportedAttribute error by adding support for MOI.RawOptimizerAttribute

[ZedongPeng]

Description

This PR adds support for MOI.RawOptimizerAttribute to the OptimizerCache.

Previously, attempting to pass solver-specific parameters (such as "l_inf_ruiz_iterations") via JuMP’s set_optimizer_attribute would fail because OptimizerCache did not have the necessary methods to store or retrieve raw attributes, resulting in a MathOptInterface.UnsupportedAttribute error.

Reproduction of the Issue

Before this fix, running the following code resulted in a generic LoadError:

using JuMP
import MathOptInterface as MOI
using cuPDLPx

model = read_from_file("2club200v15p5scn.mps.gz")
undo = relax_integrality(model);

println("Read MPS succeed.")
set_optimizer(model, cuPDLPx.Optimizer)
set_optimizer_attribute(model, "verbose", true)
# The line below previously caused the crash
set_optimizer_attribute(model, "l_inf_ruiz_iterations", 0)
set_optimizer_attribute(model, "iteration_limit", 200)

optimize!(model)
println(solution_summary(model))

Output

ERROR: LoadError: MathOptInterface.UnsupportedAttribute{MathOptInterface.RawOptimizerAttribute}: Attribute MathOptInterface.RawOptimizerAttribute("l_inf_ruiz_iterations") is not supported by the model.
Stacktrace:
  [1] throw_set_error_fallback(model::cuPDLPx.OptimizerCache, attr::MathOptInterface.RawOptimizerAttribute, value::Int64; error_if_supported::MathOptInterface.SetAttributeNotAllowed{…})
    @ MathOptInterface ~/.julia/packages/MathOptInterface/03Qtw/src/attributes.jl:631
  ...
  [7] set(m::Model, attr::MathOptInterface.RawOptimizerAttribute, value::Int64)
    @ JuMP ~/.julia/packages/JuMP/e83v9/src/optimizer_interface.jl:1264

Hi @blegat . I implemented the storage using model.ext, but I am not sure if this is the best practice (or if there is a preferred way to handle this in MOI). Could you give it a look when you have time? Thank you so much.

[blegat]

You should throw(MOI.UnsupportedAttribute(param)) if itls not supported before this line