Should the decompression method go in the `ColoringProblem` or in the `ColoringAlgorithm`?

[gdalle]

In DifferentiationInterface, the structure and partition can be deduced from the context, but the decompression method (either :direct or :substitution) should be configurable by the user.

In AutoSparse backend you can give a ColoringAlgorithm.

[gdalle]

Today:

• ColoringProblem{structure,partition,decompression}
• ColoringAlgorithm{order}

Tomorrow:

• ColoringProblem{structure,partition}
• ColoringAlgorithm{decompression,order}

In any case, ColoringResult{structure,partition,decompression}