Restore support for raw attributes

[pedromxavier]

While adjusting the attribute dispatch flow for v0.1.5, support for raw attributes was not defined properly.

using JuMP, ToQUBO, DWaveNeal

# This works
model = Model(DWaveNeal.Optimizer)

set_optimizer_attribute(model, "num_reads", 8_000)

# This also works
model = Model(() -> ToQUBO.Optimizer(DWaveNeal.Optimizer))

set_optimizer_attribute(model, DWaveNeal.NumberOfReads(), 8_000)

# This does not
model = Model(() -> ToQUBO.Optimizer(DWaveNeal.Optimizer))

set_optimizer_attribute(model, "num_reads", 8_000) # error

Tasks

• [x] Add tests
• [ ] Forward MOI.get and MOI.set to the underlying solver