C4: MindtPy solver-interface quality-of-life fixes

[bernalde]

Companion to the APPSI single-tree request (Pyomo#4020); smaller concrete items:

• HiGHS is hard-coded as no-QP/QCP, so QP models silently route to the NLP solver (TODO algorithm_base_class.py:518 — revisit when APPSI HiGHS adds QP).
• Grey-box models unsupported with gurobi_persistent single tree (cut_generation.py:217 TODO).
• cyipopt dual-sign workaround duplicated x3 (single_tree.py:495, algorithm_base_class.py:1165,1463) pending upstream cyipopt#2831 — consolidate and track.
• Solution-pool APPSI rejection silently rewrites the user's mip_solver (surprising side effect; at minimum warn loudly).
• Dual-bound patching after no-good cuts relies on a fragile stored_bound[primal_bound] dict lookup ("Bound fix failed." on KeyError).

Part of roadmap epic #2 (item C4).