Use `guesses` for state priority in initialization system

[aml5600]

Is your feature request related to a problem? Please describe.

When generating an initialization system it would be great if there was a priority given to the provided guess states that they will end up in the simplified system as states, rather than observables. I provide guesses for (suspected) unknown states given that as the model developer, I would have some expert knowledge about the system.

Given the somewhat randomly chosen unknowns for the simplified system, I really don't have any way to provide a reasonable guess to the for the problem's u0.

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Additional context

[aml5600]

FYI @AayushSabharwal