Consider allowing state appending with States.from_file() and States.from_future()

[arcondello]

dwave-optimization/dwave/optimization/states.pyx

Lines 158 to 159 in eae15af

	if not replace:
	raise NotImplementedError("appending states is not (yet) implemented")

Right now there is no way to load states from a file or future without replacing the states already present. It would be useful to be able to instead append.