Add output objective semantics to Instance and ParametricInstance

[termoshtt]

Summary

• Add a v2 OutputObjective to Instance and ParametricInstance so the active solver formulation can differ from the objective reported by evaluate() and evaluate_samples(). Parameter materialization and state reconstruction preserve that output meaning; v1 serialization rejects models that it cannot represent losslessly.
• Make objective conversion an explicit Preparation phase, add canonical QUBO/HUBO input classes and policy factories, and define to_qubo() / to_hubo() as in-place Preparation followed by format extraction. Whole-problem as_minimization_problem() / as_maximization_problem() conversions keep their original meaning.
• Map solver optimality through the output-objective contract in the HiGHS, PySCIPOpt, and Python-MIP adapters. A finite-penalty optimum remains Optimality.Unspecified when it does not prove optimality for the reported objective.

Behavior change

QUBO/HUBO conversion now keeps the prepared minimization energy as the active Instance, while evaluated results retain the input instance's output semantics:

from ommx import DecisionVariable, Instance, Sense

x = DecisionVariable.binary(0)
instance = Instance.from_components(
    sense=Sense.Maximize,
    objective=x,
    decision_variables=[x],
    constraints={0: x == 1},
)

qubo, offset = instance.to_qubo(uniform_penalty_weight=2.0)
state = {0: 0.0}

# Solver-facing energy: minimize -x + 2 (x - 1)^2.
assert instance.sense == Sense.Minimize
assert instance.objective.evaluate(state) == 2.0

# User-facing output: the input Maximize / x objective.
solution = instance.evaluate(state)
sample_set = instance.evaluate_samples({0: state})
assert solution.sense == Sense.Maximize
assert solution.objective == 0.0
assert sample_set.sense == Sense.Maximize
assert sample_set.objectives[0] == 0.0

This intentionally corrects the Python SDK v2 behavior, which restored the active sense but evaluated the final penalized energy. Returned QUBO/HUBO coefficients retain their existing meaning. The equivalent editable workflow is prepare(InstanceClass.qubo(), PreparationPolicy.for_qubo(...)) followed by as_qubo_format(); HUBO has matching helpers.