R2N : sub_kwargs fails and allocates

[MaxenceGollier]

RegularizedOptimization.jl/src/R2N.jl

Line 229 in d6f054c

sub_kwargs::Dict{Symbol} = Dict(),

This line produces the error

julia> sub_kwargs::Dict{Symbol} = Dict()
ERROR: MethodError: no method matching (Dict{Symbol})(::Dict{Any, Any})
The type `Dict{Symbol}` exists, but no method is defined for this combination of argument types when trying to construct it.

when somebody tries to call R2N through solve!.

Moreover it produces allocations as well as type instabilities when we call solve!(args..; sub_kwargs...) because it has to copy sub_kwargs into a NamedTuple.
It was introduced in #172