Make circuit validation feasibility-aware and energy-consistent for constrained/MAXIMIZE problems

[Copilot]

PR #67’s validation update still compared against objective_value() and relied on exception handling for infeasible states, which breaks MAXIMIZE semantics and misses problems that mark infeasibility via isFeasible(). This change makes validation consistent with circuit construction (energy) and explicit feasibility rules.

• Phase expectation source

  • Use problem.energy(bitstring) for feasible states, matching canonical phase-separator semantics across MINIMIZE and MAXIMIZE objectives.
  • Remove exception-driven validity detection from validation flow.

• Feasibility-aware state handling

  • Use problem.isFeasible(bitstring) to decide inclusion in validation.
  • Add omit_infeasible_states support that excludes infeasible basis states from phase-error checks.
  • Add guard for degenerate masks (no selected states).

• Parameter clarity and compatibility

  • Introduce infeasible_energy as the explicit placeholder value for infeasible states.
  • Keep global_phase as a deprecated alias with warning + conflict check to avoid ambiguous inputs.

• Validation regression coverage

  • Add targeted tests for constrained behavior: pass when infeasible states are omitted, fail when included with mismatched placeholder energy.

ok, report = check_phase_separator_exact_problem(
    problem,
    t=1.0,
    omit_infeasible_states=True,
    infeasible_energy=0.0,
)

[fgfuchs]

approved