Error with SolverBenchmark

I am trying to benchmark solvers on a Diagonal Quasi-Newton Model. I get two issues:

1. I get `type DiagonalQNModel has no field counters`
2. When giving a Quasi-Newton Model to Ipopt, I get `MethodError : no method matching hess_structure!(::NLPModelsModifiers.DiagonalQNModel{...},...)`

Here is an example
```
using BenchmarkTools, Dates, LinearAlgebra, JLD2

using Percival, NLPModels, NLPModelsIpopt, SolverBenchmark, SolverCore, NLPModelsModifiers
using OptimizationProblems, ADNLPModels, OptimizationProblems.ADNLPProblems

meta = OptimizationProblems.meta
problem_names = meta[(meta.has_equalities_only.==1).&(meta.has_bounds.==0).&(meta.has_fixed_variables.==0).&(meta.variable_nvar.==0), :name]
problem_list = (SpectralGradientModel(eval(Meta.parse(name))(), σ=1.0) for name in problem_names)

solvers = Dict(
:ipopt =>
nlp -> ipopt(
nlp,
),
:percival =>
nlp -> percival(
nlp,
),
)

stats = bmark_solvers(solvers, problem_list)
```

There is no reason for not having a `hess_structure!` method at least for the DiagonalQNModel type because it is trivial. I can also add the counters as a field of the different structures if you think it is appropriate.

Start by running the supplied SolverBenchmark example and inspect DiagonalQNModel, its counters handling, and the hess_structure! entry point. Compare the model interfaces used by bmark_solvers and Ipopt to determine the expected methods and fields. Done means the benchmark runs without the reported counters error and Ipopt accepts the quasi-Newton model.

Scritto dal modello di indicizzazione a partire dal testo della issue.