Eliminate useless allocation for diagonal quasi-Newton operators

[MohamedLaghdafHABIBOULLAH]

@dpo With these changes, push! for diagonal QN operator should no longer allocate memory.

julia> using LinearOperators

julia> D = DiagonalAndrei(ones(2));

julia> s0 = sqrt(3) * ones(2)

julia> y0 = sqrt(2) *ones(2)

julia> @wrappedallocs push!(D, s0, y0)
0

julia> D = DiagonalPSB(ones(2))

julia> @wrappedallocs push!(D, s0, y0)
0

julia> D = SpectralGradient(1., 2);

julia> @wrappedallocs push!(D, s0, y0)
0

[github-actions]

Package name	latest	stable
CaNNOLeS.jl
DCISolver.jl
FletcherPenaltySolver.jl
JSOSolvers.jl
Krylov.jl
NLPModels.jl
NLPModelsModifiers.jl
PROPACK.jl
Percival.jl
QuadraticModels.jl
SolverTools.jl

[dpo]

We're still missing @wrappedallocs and unit tests, right?

[MohamedLaghdafHABIBOULLAH]

@dpo I have added wrappedallocs and a unit test for the new versions of diagonal push, and I removed the unused iterators