future work for MIQCQP support

Here is a short list of items that would be nice to include (eventually) for MIQCQP support.

• Support for more solvers (CPLEX, MOSEK, Artelys Knitro?)
  • miqcqps_cplex()
  • miqcqps_knitro()
  • miqcqps_mosek()
• Support for running a pricing stage after the mixed integer solve, in order to compute shadow prices (like the miqps_<solver> functions do).
  • With skip_prices and price_stage_warn_tol option support.
• Support for mip_gap and mip_gap_abs options.
• Support for mip_gap field in output.
• Make miqcqps_master() call miqps_master() explicitly for a problem with no quadratic constraints (I think).
  • Same for qcqps_master() and qps_master().

Start by reviewing the existing miqps_(), miqcqps_master(), qcqps_master(), and qps_master() entry points to understand the current solver and pricing behavior. Select and scope one item from the list, then define its supported options, output fields, and solver behavior before implementation. Done means the selected MIQCQP capability is implemented and covered by the relevant tests.